T cell growth factor

ABSTRACT

The present invention relates generally to a T cell growth factor. More particularly, the present invention relates to a T cell growth factor which comprises a glycoprotein which supports interleukin 2- and interleukin 4-independent growth of helper T cells especially from murine and human sources and further which is capable of augmenting proliferation of IL3- or IL4-responsive cells. Even more particularly, the present invention relates to the helper T cell growth factor P40, pharmaceutical compositions thereof, antibodies thereto and recombinant DNA clones thereof. The present invention also contemplates a method for inducing the proliferation of helper T cells as well as IL3- and Il4-responsive cells. The helper T cells growth factor contemplated herein is useful in the stimulation of specific cells in the immune system, either alone or in combination with IL3 or IL4.

This application is a a continuation-in-part of Ser. No. 408,155 filed Sep. 15, 1989, now U.S. Pat. No. 5,157,112 which is a continuation-in-part of Ser. No. 246,482 filed Sep. 19, 1988, now U.S. Pat. No. 5,208,218.

FIELD OF THE INVENTION

The present invention relates generally to a T cell growth factor. More particularly, the present invention relates to a mammalian T cell growth factor which is a glycoprotein capable of supporting interleukin 2- and interleukin 4-independent growth of helper T cells. This factor is further capable of augmenting proliferation of IL3- and IL4-responsive cells. Even more particularly, the present invention relates to the helper T cell growth factor P40, pharmaceutical compositions thereof, antibodies thereto, and nucleic acid encoding P40. The present invention also contemplates a method for inducing the proliferation of helper T cells as well as IL3- and IL4-responsive cells. The helper T cell growth factor contemplated herein is useful in the stimulation of specific cells in the immune system.

BACKGROUND OF THE INVENTION

Many cytokines are polypeptides which directly or indirectly mediate host defense mechanisms and/or which mediate tissue growth differentiation. Cytokines have been recognized which mediate host defense against cancer and/or infection. Such cytokines include the interferons (IFN-α, IFN-β and IFN-γ), tumor necrosis factor (TNF-α), lymphotoxin (TNF-β), the interleukins (IL1, 2, 3, 4, 5 and 6), leukoregulin, natural killer cell cytotoxic factor (NKCF), transforming growth factor (TGF), colony stimulating factors (CSF) such as macrophage (M-CSF), granulocyte (G-CSF) and macrophage, granulocyte-CSF (G,M-CSF) and oncostatin M. Each of the aforementioned cytokines have unique characteristics and a unique range of antiproliferative, cytostatic, antiviral or growth regulatory activity.

Several cytokines are synthesized by leukocytes commonly in response to stimulation by microorganisms, antigens or mitogens. This has been observed in vitro. Following this stimulation in cell culture, the supernatant fluid is retrieved and cytokine activity identified, isolated and further characterized. In recent years, it has become increasingly clear the IL2 is not the only factor controlling T cell growth. Indeed, several cytokines, including IL4 (Fernandez-Botran et al., Proc. Natl. Acad. Sci. USA 83: 9689-9693, 1986; Lichtman et al., Proc. Natl. Acad. Sci. USA 84: 824-827, 1987) G,M-CSF (Woods et al., J. Immunol. 138: 4293-4297, 1987); Kupper et al., J. Immunol. 138: 4288-4292, 1987) and, in a human system, the combination of IL1 and IL6 (Houssiau et al., Eur. J. Immunol. 18: 653-656, 1988), have now been shown to induce IL2-independent T cell proliferations. Consequently, the regulation of T cell growth is more complex then originally thought, although IL2 is a potent and broadly active T cell growth factor.

An important subset of T cells is the helper T cell (T_(H)). At least two types of helper T cells have been identified on the basis of functional criteria. One type of T_(H) cell (T_(H) 1) helps B cells in a linked, antigen-specific manner, and is required early in the response. Another type of T_(H) (T_(H) 2) helps B cells in a nonlinked manner and is required later in the response.

Several years ago, a collection of helper T cell lines from lymph nodes of antigen-primed mice was obtained using the procedure described by Corradin et al., J. Immunol. 119: 1048-1053, 1977. These cell lines were initiated by culture in the presence of antigen and were subsequently maintained, without addition of exogenous growth factors, by regular feeding with antigen and irradiated splenic antigen-presenting cells. Most of these cells produce large amounts of IL3, IL4, IL5 and IL6, but no IL2 and, therefore, belong to the T_(H) 2 type defined by Mosmann et al., J. Immunol. 136: 2348-2357, 1986.

In accordance with the present invention, it is surprisingly discovered that two clones derived from the above-mentioned cell lines proliferated in response to their own conditioned medium in the absence of antigen and feeder cells. The subject invention relates to a novel T cell growth factor distinct from other known cytokines. The new growth factor is useful as a therapeutic compound to stimulate proliferation of helper T cells.

SUMMARY OF THE INVENTION

The present invention is directed to a mammalian T cell growth factor Which supports interluekin 2-independent and interleukin 4-independent growth of helper T cells, and is preferably obtained from mouse or human sources.

More particularly, this T cell growth factor is a protein having the identifiable characteristics of P40, derivatives or fragments thereof and the further capability of augmenting proliferation of IL3- and IL4-responsive cells. Methods of isolating P40, its derivatives and fragments are also provided.

Another aspect of the present invention relates to a pharmaceutical composition comprising an effective amount of P40, a derivative or fragment thereof and a pharmaceutically acceptable carrier useful in the stimulation of specific cells in the immune system. Optionally, these compositions may also contain IL3 or IL4.

Still another aspect of the present invention relates to antibodies specific to P40, or an antigenic derivative or an antigenic fragment thereof, useful in diagnostic assays for P40.

Yet another aspect of the present invention relates to a recombinant DNA molecule and expression vectors encoding the polypeptide portion of mammalian P40, a derivative or a fragment thereof, thereby providing a convenient source of recombinant P40.

Still yet another aspect of the present invention contemplates a method of proliferating helper T cells which comprises incubating said cells with a proliferating effective amount of P40 or a derivative thereof for a time and under conditions sufficient for said cells to proliferate.

A still further aspect of this invention relates to a method of proliferating IL3- or IL4-responsive cells by administering a combination of P40 and IL3 or IL4 to a mammal, especially a human, for a time and under conditions sufficient to stimulate said cells to proliferate.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graphical representation depicting long-term antigen-independent T cell growth induced by helper T cell supernatant (SN). TUC2.15 cells are grown without feeder cells and antigen in normal medium (□), in medium supplemented with IL2 (20 U/ml, ▪) or witho TUC2.15 SN (5% v/v, ▴).

FIG. 2 is a graphical representation depicting purification of P40. TUC7.51 supernatants is fractioned sequentially on an Ultrogel AcA65 gel filtration column (A), a TSK-phenyl hydrophobic interaction column (B), a Mono-Q anion exchange column (C) and Cl-reversed phase column (D). The shaded area represents P40 activity. Molecular mass standards shown in panel A are bovine serum albumin (BSA, 67 kDa), natural IL5 (45 kDa) and recombinant mouse IL6 (22 kDa).

FIG. 3 is a graphical representation depicting growth factor activity of purified P40. TS1 cells (3×10³ cells/well) are cultivated in the presence of increasing doses of purified P40. After 3 days, cells numbers are evaluated by measuring hexosaminidase levels.

FIG. 4 illustrates the purity of P40 and its extent of glycosylation. Panel A is a photograph showing silver-strained NaDodSo₄ /PAGE of purified P40. The sample is run under reducing conditions. Panel B is an autoradiograph of ¹²⁵ I-P40 treated with various glycosylases. Mr of standards is given kDa.

FIG. 5 is a graphic illustration of the sequencing strategy of the murine P40 gene.

FIG. 6 is a graphic illustration of the expression strategy of the murine P40 gene.

FIG. 7 shows the amino acid sequence of murine P40 obtained by chemical sequencing and the various peptides used in obtaining this sequence.

FIG. 8 is a graphic illustration of the separation of endoproteinase Asp-N peptides of Cm-P40 by RP-HPLC.

FIG. 9 is a graphic illustration of a multi-wavelength plot of the HPLC profile of FIG. 8 using a photodiode array detector at wavelengths of (A) 290 nm, (B) 280 nm, (C) 254 nm and (D) 215 nm.

FIG. 10 is a graphic illustration of a derivative spectral analysis of endoproteinase Asp-N peptide D1 with the zero other spectrum indicated by (---) and the second order spectrum indicated by (--).

FIG. 11 is a graphic illutration of the microbore RP-HPLC separation of peptides of Cm-P40 derived from digestion with various proteases. Panel A shows the peptides from S. aureus V8 protease digestion of Cm-P40 endoproteinase Asp-N peptide D3. Panel B shows the peptides from a chymotrypsin digestion of Cm-P40. Panel C shows the peptides from a trypsin digestion of Cm-P40.

FIG. 12 is a graphic illustration of the elution profile of the blocked amino terminal peptide D1 and related synthetic peptides on RP-HPLC. Z indicates pyroglutamic acid.

FIG. 13 depicts a restriction cleavage map and the exon/intron organization of the human and mouse P40 genes. Closed boxes represent coding regions, and numbers indicate their respective length in base pairs. Open box corresponds to 5' untranslated region. Arrows represent direction and extent of sequence analysis. Restriction endonuclease sites used for sequencing are indicated: A, AccI; B, BamHI; Bg, BglII; El, EcoRI; EV, EcoRV; H, HindIII; N, NcoI; P, PstI; S, SmaI; Ss, SstI; X, XbaI.

FIGS. 14A, B and C show a complete nucleotide sequence coding for the human P40 gene. The sequence begins at FIG. 14A, continues through FIG. 14B and concludes at FIG. 14C. Nucleotide numbering is relative to the initiator ATG. Amino acid sequences of the coding regions are given in one-letter code. Potential regulatory or signal sequences are underlined.

FIGS. 15A, B and C show a complete nucleotide sequence coding for the mouse P40 gene. The sequence begins at FIG. 15A, continues through FIG. 15B, and ends at FIG. 15C. Nucleotide numbering is relative to the initiator ATG. Amino acid sequences of the coding regions are given in one-letter code. Potential regulatory or signal sequences are underlined.

FIG. 16. shows a comparison of the human and mouse P40 5'-(A) and 3'- untranslated regions (B). In (A), nucleotides are numbered 3' to 5' relative to the first nucleotide of the ATG start codon. Transcription starts are underlined and conserved consensus motifs are boxed. In (B), nucleotides are numbered 5' to 3' starting with the first nucleotide following the stop codon. Nucleotide sequences potentially involved in mRNA degradation are underlined and presumptive polyadenylation signals are double-underlined.

FIG. 17 shows an autoradiograph illustrating the kinetics of P40 in activated human peripheral blood mononuclear cells (PBMC). PBMC were stimulated with PMA and A23187, and RNA was extracted at the indicated times. Northern blots were hybridized with a ³² P-labeled human P40 cRNA and exposed overnight.

FIG. 18 shows a dot blot illustrating the ability of various stimuli to induce P40 in human PBMC. Unfractionated PBMC were stimulated as described in Example 1. Three-fold dilutions of cytoplasmic RNA were blotted on nitrocellulose and hybridized with P-labeled P40 cDNA.

FIG. 19 illustrates the expression of P40 mRNA in CD4⁺ T cells. Human PBMC were fractionated as described in Example 1 and stimulated for 24 hours with PHA and PMA. Three-fold dilutions of cytoplasmic RNA were blotted onto nitrocellulose and hybridized with ³² P-labeled P40 cDNA. RNA was prepared from 15 and 10×10⁶ cells in left and right panels, respectively.

FIG. 20. is a graphic illustration depicting the expression and biological activity of recombinant human P40. The left panel shows survival curves of a human T cell line (EL) incubated in medium without factors (□), or in medium supplemented with saturating concentrations of semi-purified baculovirus-derived human P40 (), with a control preparation derived from cells infected with wild-type baculovirus (◯), with purified mouse recombinant P40 (▪) or with human IL-4 (▴). All cultures were seeded with 50,000 cells on day 0. The right panel shows SDS-PAGE of ³⁵ S-labeled semi-purified recombinant human P40 (left lane) and of a control preparation (right lane).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a mammalian T cell growth factor which comprises a protein which supports, or is capable of supporting, interleukin 2 (IL2)-independent and interleukin 4 (IL4)-independent growth of helper T cells in the absence of antigen. In accordance with the present invention and using the methods contained herein, said T cell growth factor is biologically pure. By biologically pure is meant a composition comprising said T cell growth factor. The composition may comprise homogeneous T cell growth factor or may consist essentially of T cell growth factor. As used in the specification and appended claims, supporting IL2-independent and IL4-independent growth of helper T cells refers to the ability for said cells to proliferate in the absence of IL2 and/or IL4. This feature distinguishes the subject growth factor from others presently known. In accordance with the present invention, this ability is due to a novel and heretofore unknown T cell growth factor. Hereinafter, said growth factor is referred to as P40. As defined herein, derivatives of P40 encompass synthetic and naturally occurring amino acid substitutions, deletions and/or insertions as will be apparent to the skilled artisan. For example, non-essential amino acid deletions, i.e., deletion of amino acids which do not affect the activity of P40 are obtainable by genetic engineering means.

Furthermore, fragments of P40 are contemplated by the present invention. These fragments are peptides obtained from the P40 protein and may be prepared by proteolysis of purified P40. The peptides are purified by conventional means such as HPLC chromatography and the like, and are useful in determining the P40 amino acid sequence, in preparing antibodies to specific domains of P40 and in identifying the P40 domains involved in stimulating T cell growth.

An antigenic derivative of P40 is defined to be a portion of P40 which is capable of reacting with an antibody specific to P40. All such derivatives are encompassed by the subject invention.

Accordingly, P40 is a protein, and more particularly, a glycoprotein, capable of supporting long-term IL2-independent and IL4-independent growth of helper T cell lines in the absence of antigen, and is isolated from helper T cell lines, especially mammalian lines like murine and human helper T cell lines. P40 is functionally distinct from all known interleukins and colony-stimulating factors. P40 is purified from the supernatant (SN) of lectin-stimulated mouse helper T cell lines to a specific activity of from about 10 U/mg to about 10¹⁰ U/mg, but generally to about 10⁸ U/mg and characterized as a basic (pI≈10 for murine P40) single chain protein with an Mr of from about 30 to about 40 kDa.

P40 can be purified from the supernatant fluid of antigen stimulated mouse helper T cell clones (TUC2.15 and TUC7.51). Briefly, the supernatant fluid is concentrated and applied to a TSK-phenyl chromatography column. Fractions with growth factor activity on factor-dependent TS1 cells are pooled, further fractionated on a Mono-Q chromatography column, and the resulting active fractions applied to a C1 reversed-phase HPLC column. Pure murine P40 is eluted at a concentration of about 35% acetonitrile.

Two observations indicate that P40 is a glycoprotein: (i) its heterogeneous migration pattern in NaDodSO₄ /PAGE and (ii) its binding to lentil lectin, which points to the presence of N-linked carbohydrate side chains. Consistent with this observation, a number of potential N-glycosylation sites (Asn-X-Thr motif) have been identified in the protein sequence. Moreover, additional evidence for extensive glycosylation of the molecule is obtained in experiments with N-glycanase treatment, which reduced the Mr of P40 to about 15 kDa. P40 is a stable molecule whose biological activity is not altered after exposure to NaDodSO₄, acid pH or acetonitrile. By contrast, its activity is destroyed by 2-mercaptoethanol, which suggests that intramolecular disulfide bridges play an important role in maintaining appropriate folding of the molecule. P40 is also distinguished from known proteins on the basis of its complete amino acid sequence. The DNA and amino acid sequence of murine P40 and human P40 are described herein and indicate that the two proteins are 55% homologous.

In addition to the aforementioned distinguishing structural characteristics of P40, it also differs functionally from IL2. P40 is completely inactive on cytolytic T cell clones under conditions where their response to IL2 is very strong; conversely, IL2 fails to support long-term antigen independent growth of helper T cell lines, whereas P40 is very active in this system. To date, long-term growth of helper cells in response to P40 means greater than two months and may be indefinite. In contrast with these differences, a correlation is observed between the sensitivity of helper T cell lines to P40 and IL4, indicating that T cell activation by these two molecules is similarly regulated. However, the range of activities of IL4, which also stimulates the growth of a variety of IL3-dependent cell lines and of cytolytic T cells (Mosmann et al., Proc. Natl. Acad. Sci. USA 83: 5654-5658, 1986; Widmer et al., Nature 326: 795-798, 1987) is broader than that of P40, indicating that the functional overlap between the two factors, IL4 and P40, is only partial.

Another advantage of the subject T cell growth factor, P40, is the surprising discovery that P40 is specific for helper T cell lines. This indicates the existence of a growth-stimulatory mechanism restricted to the helper T cell subset. Such a mechanism is important for maintaining the balance between the supply of helper T cell products like IL2 and IL4 and their increased consumption by other lymphocytes activated in the course of the immune response.

While investigating the range of P40 activity, it was surprisingly discovered that P40 augments proliferation of IL3- or IL4-responsive cells in a synergistic manner. As used herein, IL3- add IL4-responsive cells are immune system cells which proliferate in response to IL3 or IL4, respectively. These cells may include IL3-dependent cells or IL4-dependent cells, but are not limited thereto. IL3-responsive cells include helper T cells, stem cells, mast cells, eosinophils, neutrophils, monocytes, megakaryocytes, basophils, and erythropoid cells. IL4-responsive cells include helper T cells, activated cytotoxic T cells, macrophages, mast cells and B cells (Smith, K. A., Biotechnology 7: 661-667, 1989).

Hence there is a strong synergism with respect to growth for cells stimulated with P40 and IL3, or P40 and IL4. In a thymidine uptake assay which measures cellular proliferation, the combination of cytokines P40 and IL3, or P40 and IL4, can stimulate thymidine uptake by a factor ranging from about 4 to 40 above the stimulatory effect of any one of the cytokines. In general, the synergism between P40 and IL3, or P40 and IL4, is dose dependent and cell line dependent. For these proteins and a given cell line, suboptimal doses of P40 range from about 1-25% of optimal P40 doses, suboptimal doses of IL4 range from about 5-30% of optimal IL4 doses, and close to optimal doese of IL3 range from about 70-100% of optimal IL3 doses. This synergism provides a further method to stimulate proliferation of IL3- and IL4-responsive cells, especially helper T cells, and is therapeutically useful in treating immune deficiencies, especially those diseases or disease states which benefit from proliferation of specific immune cells such as AIDS, or even from general proliferation of immune cells.

Further investigation of the biological properties of mammalian P40 show that this cytokine has a broader spectrum of activities including enhancement of cell survival, and may effect a wider variety of cell types, generally of hemapoetic lineage. Human P40 prolonged survival of human T cell lines maintained in culture in the presence of PHA, irradiated PBMC as feeders, and IL-4. Murine P40 also increased cell survival of mouse T cell lines, and in one instance, a human T cell line (see Example 15). Human P40 was apparently not active on mouse P40-dependent cell lines.

P40 does not appear to be constitutively expressed but can generally be induced by T cell mitogens or with a combination of phorbal myristate acetate (PMA) and the calcium ionophore A23187. T cell mitogens which induced P40 in PBMC include phytohemagglutinin (PHA) and anti-CD3 antibodies. Co-culturing PBMC with either of these mitogens and PMA further enhanced P40 expression, especially human P40. No induction occured when PBMC were treated with PMA alone, lipopolysaccharide or Staphylococcus aureus strain Cowan 1. In all cases expression was monitored by measuring the levels on P40 mRNA by dot blot analysis.

To investigate the pattern of P40 expression in human PBMC, cells were fractionated into rosetting cells (representing primarily T cells) and non-rosetting cells. The rosetting cells were then further divided into CD4⁺ and CD8⁺ T cells by fluorescence-activated cell sorting. Expression of P40 was detected in rosetting PBMC and CD4⁺ T cells, but not in non-rosetting PBMC or CD8⁺ T cells. These results indicate that P40 is primarily expressed in helper T cells (CD4⁺ cells) in humans as previously found for murine P40.

It is within the scope of the present invention to include biologically pure P40 in addition to homogenous and heterogenous compositions thereof. Thus in accordance with the present invention, supernatant (SN) from a helper T cell line not requiring antigen or feeders comprises P40. This SN is able to induce cell proliferation without further requirement for antigen or feeder cells. As further described in Example 1, the proliferation activity is not inhibited by either anti-IL4 or anti-IL2 receptor antibodies, indicating that said activity is mediated neither directly nor indirectly by these molecules. The active ingredient in the aforementioned SN is shown to be, in accordance with the present invention, P40. The SN is active on the test cells, TS1, inducing half-maximal proliferation at dilutions ranging of from about 10⁻⁶ to about 10⁻² (v/v), and generally ranging from about 10⁻⁵ to about 10⁻⁴ (v/v). Thus, in accordance with the present invention, the novel T cell growth factor P40 is active in biologically pure form and in homogenous and heterogeneous compositions. As exemplified herein, SN fluid is a form of heterogeneous composition of P40. Homogeneous compositions are exemplified herein to include pharmaceutical compositions containing homogeneous preparations of P40, its active derivatives or fragments, and the like.

The T cell growth factor P40 is contemplated herein to be useful in stimulating the proliferation of T helper cells in mammals. In a preferred embodiment, P40 is particularly useful in stimulating certain subsets of T helper cells in mammals. Accordingly, P40 is a new and useful therapeutic compound capable of stimulating specific cells within the immune cells. For example, this is particularly important for human patients carrying defects in certain subsets of T helper cells as may be the case with various AIDS patients or immune compromised patients. It should also be noted that of the many advantages of the present invention, the proliferation of helper T cells by P40 will have the additional effect of allowing increased amounts of other cytokines to be produced. Accordingly, the present invention also contemplates a method of treatment of immune deficiency compromising the administration of a proliferating effective amount of P40, an active derivative, or an active fragment thereof, for a time and under conditions sufficient to effect proliferation of helper T cells. In accordance with the present invention, the time required for the proliferation of helper T cells ranges from about two days to about seven days.

Accordingly, the subject invention contemplates a method for inducing and maintaining the proliferation of helper T cells, and preferable, certain subsets thereof, in a mammal which comprises administering to said mammal a proliferating-effective amount of a pharmaceutical composition containing P40, an active derivative or fragment thereof, for a time and under conditions sufficient for said cells to proliferate. Additionally, a method for inducing and maintaining the proliferation of helper T cells, and preferably certain subsets thereof, in a mammal, is contemplated by this invention in which a nucleic acid molecule encoding P40 is introduced into a T cell in such a manner that said nucleic acid molecule is expressed intracellularly, but extrachromosomally of said cell or following integration into the genome of said cell. In this case, the nucleic acid molecule is carried to said T cell and transferred into said cell by a second nucleic acid molecule (e.g., various viruses). The first nucleic acid molecule is manipulated such that it contains the appropriate signals for expression. That is, in accordance with the present invention, a method for proliferating T helper cells in a mammal is contemplated comprising administering a first nucleic acid molecule encoding P40, said nucleic acid molecule being contained in a pharmaceutically acceptable second nucleic acid carrier molecule such that said first nucleic acid molecule enters a T cell and is either maintained extrachromosomally or integrated into the genome of said target all in such a manner that said first nucleic acid molecule is expressed so as to produce an effective amount of P40. By nucleic acid molecule is meant the nucleotide sequence which encodes, directly or indirectly, P40 or a derivative thereof. A nucleic acid molecule is defined herein to mean RNA or DNA.

The active ingredients of a pharmaceutical composition comprising P40 are contemplated to exhibit excellent and effective therapeutic activity, for example, in the treatment of immune compromised diseases in mammals. Thus the active ingredients of the therapeutic compositions comprising P40 exhibit helper T cell proliferative activity when administered in therapeutic amounts which depend on the particular disease. For example, from about 0.5 ug to about 2000 mg per kilogram of body weight per day may be administered. The dosage regimen may be adjusted to provide the optimum therapeutic response. For example, several divided doses may be administered daily or the dose may be proportionally reduced as indicated by the exigencies of the therapeutic situation. A decided practical advantage is that the active compound may be administered in a convenient manner such as by the oral, intraveneous (where water soluble), intramuscular, subcutaneous, intranasal, intradermal or suppository routes. Depending on the route of administration, the active ingredients which comprise P40 may be required to be coated in a material to protect said ingredients from the action of enzymes, acids and other natural conditions which may inactivate said ingredients. For example, the low lipophilicity of P40 may allow it to be destroyed in the gastrointestinal tract by enzymes capable of cleaving peptide bonds and in the stomach by acid hydrolysis. In order to administer P40 by other than parenteral administration, P40 should be coated by, or administered with, a material to prevent its inactivation. For example, P40 may be administered in an adjuvant, co-administered with enzyme inhibitors or in liposomes. Adjuvants contemplated herein include resorcinols, non-ionic surfactants such as polyoxyethylene oleyl ether and n-hexadecyl polyethylene ether. Enzyme inhibitors include pancreatic trypsin inhibitor, diisopropylfluorophosphate (DFP) and trasylol. Liposomes include water-in-oil-in-water P40 emulsions as well as conventional liposomes.

The active compounds may also be administered parenterally or intraperitoneally. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof, and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms.

The pharmaceutical forms suitable for injectable use include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersion. In all cases the form must be sterile and must be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, liquid polyethylene glycol, and the like), suitable mixtures thereof and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The preventions of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin.

Sterile injectable solutions are prepared by incorporating the active compounds in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum-drying and the freeze-drying technique which yield a powder of the active ingredient plus any additional desired ingredient from previously sterile-filtered solution thereof.

When P40 is suitably protected as described above, the active compound may be orally administered, for example, with an inert diluent or with an assimilable edible carrier, or it may be enclosed in hard or soft shell gelatin capsule, or it may be compressed into tablets, or it may be incorporated directly with the food of the diet. For oral therapeutic administration, the active compound may be incorporated with excipients and used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. Such compositions and preparations should contain at least 1% of active compound. The percentage of the compositions and preparations may, of course, be varied and may conveniently be between about 5 to about 80% of the weight of the unit. The amount of active compound in such therapeutically useful compositions is such that a suitable dosage will be obtained. Preferred compositions or preparations according to the present invention are prepared so that an oral dosage unit form contains between about 10 ug and 1000 ug of active compound.

The tablets, troches, pills, capsules, and the like, may also contain the following: a binder such as gum gragacanth, acacia, corn starch or gelatin; excipients such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid, and the like; a lubricant such as magnesium stearate; and a sweetening agent such as sucrose, lactose or saccharin may be added or a flavoring agent such as peppermint, oil of wintergreen or cherry flavoring. When the dosage unit form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier. Various other materials may be present as coatings or to otherwise modify the physical form of the dosage unit. For instance, tablets, pills or capsules may be coated with shellac, sugar or both. A syrup or elixir may contain the active compound, sucrose as a sweetening agent, methyl and propylparabens as preservatives, a dye and flavoring such as cherry or orange flavor. Of course, any material used in preparing any dosage unit form should be pharmaceutically pure and substantially non-toxic in the amounts employed. In addition, the active compound may be incorporated into sustained-release preparations and formulations.

It is especially advantageous to formulate parenteral compositions in dosage unit form for ease of administration and uniformity of dosage. Dosage unit form as used herein refers to physically discrete units suited as unitary dosages for the mammalian subjects to be treated; each unit containing a predetermined quantity of active material calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. The specification for the novel dosage unit forms of the invention are dictated by and directly dependent on (a) the unique characteristics of the active material and the particular therapeutic effect to be achieved, and (b) the limitations inherent in the art of compounding such an active material for the treatment of disease in living subjects having a diseased condition in which bodily health is impaired as herein disclosed in detail.

The principal active ingredient is compounded for convenient and effective administration in effective amounts with a suitable pharmaceutically acceptable carrier in dosage unit form as hereinbefore disclosed. A unit dosage form can, for example, contain the principal active compound in amounts ranging from 0.5 ug to about 2000 mg. Expressed in proportions, the active compound is generally present in from about 10 ug to about 2000 mg/ml of carrier. In the case of compositions containing supplementary active ingredients, the dosages are determined by reference to the usual dose and manner of administration of the said ingredients.

As used herein "pharmaceutically acceptable carrier" includes any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and adsorption delaying agents, and the like. The use of such media agents for pharmaceutical active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active ingredient, use thereof in the therapeutic compositions is contemplated. Supplementary active ingredients can also be incorporated into the compositions.

A further aspect of this invention contemplates the use of P40 with IL3 or IL4 in a method to stimulate proliferation of IL3- or IL4-responsive cells and in a method of treatment of immune deficiency. Such methods are practiced in accordance with the therapeutic methods involving only P40 and as described herein. Likewise, pharmaceutical compositions containing P40 and IL3, or P40 and IL4 are provided in accordance with those which contain P40 alone. Further in this regard, IL3 and IL4 are commercially available and are used in therapeutically effective amounts. Pharmaceutically effective amounts of P40 when used in conjunction with IL3 or IL4 are the same as when P40 is used alone. Likewise, pharmaceutically effective amounts of IL3 or IL4 amounts can be similar to those provided for P40 alone. Preferred compositions of P40 and IL3 according to the present invention are prepared so that a unit dosage form contains each protein in an amount ranging from about 0.5 ug to about 2000 mg. Preferred compositions of P40 and IL4 are likewise prepared so that a unit dosage form contains each protein in an amount ranging from about 0.5 ug to about 2000 mg. In these compositions, the relative amount of P40 to IL3 or IL4 can be varied or the same.

The present invention also relates to antibodies to P40, its derivatives or fragments. Such antibodies are contemplated to be useful in developing detection assays (immunoassays) for P40, especially during the monitoring of a therapeutic regimen and in the purification of P40. The antibodies may be monoclonal or polyclonal. Additionally, it is within the scope of this invention to include any second antibodies (monoclonal or polyclonal) directed to the first antibodies discussed above. The present invention further contemplates use of these second antibodies in detection assays and, for example, in monitoring the effect of an administered pharmaceutical preparation. Furthermore, it is within the scope of the present invention to include antibodies to the glycosylated regions of P40, and to any molecules complexed with said P40. Accordingly, in accordance with this invention, an antibody to P40 encompasses antibodies to P40, or antigenic parts thereof, and to any associated molecules (e.g., glycosylated regions, lipid regions, carrier molecules, and the like).

The P40, or parts thereof, considered herein are purified, as exemplified in Example 3, then utilized in antibody production. Both polyclonal and monoclonal antibodies are obtainable by immunization with P40, its derivatives, polypeptides or fragments, and either type of antibody is utilizable for immunoassays. The methods for obtaining both types of sera are well known in the art. Polyclonal sera are less preferred, but are relatively easily prepared by injection of a suitable laboratory animal with an effective amount of the purified P40, or parts thereof, collecting serum from the animal and isolating specific sera by any of the known immunoadsorbent techniques. Although antibodies produced by this method are utilizable in virtually any type of immunoassay, they are generally less favored because of the potential heterogeneity of the product.

The use of monoclonal antibodies in the present immunoassay is particularly preferred because of the ability to produce them in large quantities and the homogeniety of the product. The preparation of hybridoma cell lines for monoclonal antibody production derived by fusing an immortal cell line and lymphocytes sensitized against the immunogenic preparation can be done by techniques which are well known to those who are skilled in the art. (See, for example, Douillard, J. Y. and Hoffman, T., "Basic Facts About Hybridomas", in Compendium of Immunology, Vol. II, L. Schwartz (Ed.) (1981); Kohler, G. and Milstein, C., Nature 256: 495-497 (1975); European Journal of Immunology 6: 511-519 (1976); Koprowski et al., U.S. Pat. No. 4,172,124, Koprowski et al., U.S. Pat. No. 4,196,265 and Wands, U.S. Pat. No. 4,271,145, the teachings of which are herein incorporated by reference.

Unlike preparation of polyclonal sera, the choice of animal for monoclonal antibody production is dependent on the availability of appropriate immortal lines capable of fusing with lymphocytes thereof. Mouse and rat have been the animals of choice in hybridoma technology and are preferably used. Humans can also be utilized as sources for sensitized lymphocytes if appropriate immortalized human (or nonhuman) cell lines are available. For the purpose of the present invention, the animal of choice may be injected with from about 1 mg to about 20 mg of the purified P40 or parts thereof. Usually the injecting material is emulsified in Freund's complete adjuvant. Boosting injections may also be required. The detection of antibody production can be carried out by testing the antisera with appropriately labeled antigen. Lymphocytes can be obtained by removing the spleen or lymph nodes of sensitized animals in a sterile fashion and carrying out fusion. Alternatively, lymphocytes can be stimulated or immunized in vitro, as described, for example, in C. Reading, J. Immunol. Meth. 53: 261-269, 1982.

A number of cell lines suitable for fusion have been developed, and the choice of any particular line for hybridization protocols is directed by any one of a number of criteria such as speed, uniformity of growth characteristics, deficiency of its metabolism for a component of the growth medium, and potential for good fusion frequency.

Intraspecies hybrids, particularly between like strains, work better than interspecies fusions. Several cell lines are available, including mutants selected for the loss of ability to secrete myeloma immunoglobulin. Included amont these are the following mouse myeloma lines: MPC₁₁ -X45-6TG, P3-NS1-1-Ag4-1, P3-X63-Ag8, or mutants thereof such as X63-Ag8.653, SP2-0-Ag14 (all BALB/C derived), Y3-'Ag1.2.3 (rat) and U266 (human).

Cell fusion can be induced either by virus, such as Epstein-Barr or Sendai virus, or polyethylene glycol. Polyethylene glycol (PEG) is the most efficacious agent for the fusion of mammalian somatic cells. PEG itself may be toxic for cells, and various concentrations should be tested for effects on viability before attempting fusion. The molecular weight range of PEG may be varied from 1000 to 6000. It gives best results when diluted to about 20% to about 70% (w/w) in saline or serum-free medium. Exposure to PEG at 37° for about 30 seconds is preferred in the present case, utilizing murine cells. Extremes of temperature (i.e., about 45° C.) are avoided, and preincubation of each component of the fusion system at 37° C. prior to fusion gives optimum results. The ratio between lymphocytes and malignant cells is optimized to avoid cell fusion among spleen cells and a range of from about 1:1 to about 1:10 gives good results.

The successfully fused cells can be separated from the myeloma line by any technique known by the art. The most common and preferred method is to choose a malignant line which is Hypoxanthine Guanine Phosphoribosyl Transferase (HGPRT) deficient, which will not grow in an aminopterin-containing medium used to allow only growth of hybrids and which is generally ,composed of hypoxanthine 1×10⁻⁴ M, aminopterin 1×10⁻⁵ M and thymidine 3×10⁻⁵ M, commonly known as the HAT medium. The fusion mixture can be grown in the HAT-containing culture medium immediately after the fusion 24 hours later. The feeding schedules usually entail maintenance in HAT medium for two weeks and then feeding with either regular culture medium or hypoxanthine, thymidine-containing medium.

The growing colonies are then tested for the presence of antibodies that recognize the antigenic preparation. Detection of hybridoma antibodies can be performed using an assay where the antigen is bound to a solid support and allowed to react to hybridoma supernatants containing putative antibodies. The presence of antibodies may be detected by "sandwich" techniques using a variety of indicators. Most of the common methods are sufficiently sensitive for use in the range of antibody concentrations secreted during hybrid growth.

Cloning of hybrids can be carried out after 21-23 days of cell growth in selected medium. Cloning can be performed by cell limiting dilution in fluid phase or by directly selecting single cells growing in semi-solid agarose. For limiting dilution, cell suspensions are diluted serially to yield a statistical probability of having only one cell per well. For the agarose technique, hybrids are seeded in a semi-solid upper layer, over a lower layer containing feeder cells. The colonies from the upper layer may be picked up and eventually transferred to wells.

Antibody-secreting hybrids can be grown in various tissue culture flasks, yielding supernatants with variable concentrations of antibodies. In order to obtain higher concentrations, hybrids may be transferred into animals to obtain inflammatory ascites. Antibody-containing ascites can be harvested 8-12 days after intraperitoneal injection. The ascites contain a higher concentration of antibodies but include both monoclonals and immunoglobulins from the inflammatory ascites. Antibody purification may then be achieved by, for example, affinity chromatography.

The presence of P40 contemplated herein, or antibodies specific for same, in a patient's serum, tissue or tissue extract, can be detected utilizing antibodies prepared as above, either monoclonal or polyclonal, in virtually any type of immunoassay. A wide range of immunoassay techniques are available as can be seen by reference to U.S. Pat. Nos. 4,016,043; 4,424,279 and 4,018,653. This, of course, includes both single-site and two-site, or "sandwich", assays of the non-competitive types, as well as in the traditional competitive binding assays. Sandwich assays are among the most useful and commonly used assays and are favored for use in the present invention. A number of variations of the sandwich assay technique exist, and all are intended to be encompassed by the present invention. Briefly, in a typical forward assay, an unlabeled antibody is immobilized in a solid substrate and the sample to be tested brought into contact with the bound molecule. After a suitable period of incubation, for a period of time sufficient to allow formation of an antibody-antigen secondary complex, a second antibody, labeled with a reporter molecule capable of producing a detectable signal is then added and incubated, allowing time sufficient for the formation of a tertiary complex of antibody-antigen-labeled antibody (e.g., antibody-P40-antibody). Any unreacted material is washed away, and the presence of the antigen is determined by observation of a signal produced by the reporter molecule. The results may either be qualitative, by simple observation of the visible signal, or may be quantitated by comparing with a control sample containing known amounts of hapten. Variations on the forward assay include a simultaneous assay, in which both sample and labeled antibody are added simultaneously to the bound antibody, or a reverse assay in which the labeled antibody and sample to be tested are first combined, incubated and then added to the unlabeled surface bound antibody. These techniques are well known to those skilled in the art, and the possibility of minor variations will be readily apparent.

In the typical forward sandwich assay, a first antibody having specificity for P40, or antigenic parts thereof, contemplated in this invention, is either covalently or passively bound to a solid surface. The solid surface is typically glass or a polymer, the most commonly used polymers being cellulose, polyacrylamide, nylon, polystyrene, polyvinyl chloride or polypropylene. The solid supports may be in the form of tubes, beads, discs or microplates, or any other surface suitable for conducting an immunoassay. The binding processes are well-known in the art and generally consist of cross-linking, covalently binding or physically absorbing the molecule to the insoluble carrier. Following binding, the polymer-antibody complex is washed in preparation for the test sample. An aliquot of the sample to be tested is then added to the solid phase complex and incubated at 25° C. for a period of time sufficient to allow binding of any subunit present in the antibody. The incubation period will vary but will generally be in the range of about 2-40 minutes. Following the incubation period, the antibody subunit solid phase is washed and dried and incubated with a second antibody specific for a portion of the hapten. The second antibody is linked to a reporter molecule which is used to indicate the binding of the second antibody to the hapten. By "reporter molecule," as used in the present specification, is meant a molecule which, by its chemical nature, provides an analytically identifiable signal which allows the detection of antigen-bound antibody. Detection may be either qualitative or quantitative. The most commonly used reporter molecules in this type of assay are either enzymes, fluorophores or radionuclide containing molecules (i.e., radioisotopes). In the case of an enzyme immunoassay, an enzyme is conjugated to the second antibody, generally by means of glutaraldehyde or periodate. As will be readily recognized, however, a wide variety of different conjugation techniques exist, which are readily available to the skilled artisan. Commonly used enzymes include horseradish peroxidase, glucose oxidase, β-galactosidase and alkaline phosphatase, among others. The substrates to be used with the specific enzymes are generally chosen for the production, upon hydrolysis by the corresponding enzyme, of a detectable color change. For example, p-nitrophenyl phosphate is suitable for the use with alkaline phosphatase conjugates; for peroxidase conjugates, 1,2-phenylenediamine, 5-aminosalicyclic acid, or tolidine, are commonly used. It is also possible to employ fluorogenic substrates, which yield a fluorescent product rather than the chromogenic substrates noted above. In all cases, the enzyme-labeled antibody is added to the first antibody hapten complex, allowed to bind, and then to the first antibody hapten complex, allowed to bind, and then the excess reagent is washed away. A solution containing the appropriate substrate is then added to the ternary complex of antibody-antigen-antibody. The substrate will react with the enzyme linked to the second antibody, giving a qualitative visual signal, which may be further quantitated, usually spectrophotometrically, to give an indication of the amount of hapten which was present in the sample.

Alternatively, fluorescent compounds, such as fluorescein and rhodamine, may be chemically coupled to antibodies without altering their binding capacity. When activated by illumination with light of a particular wavelength, the fluorochrome-labeled antibody adsorbs the light energy, inducing a state of excitability in the molecule, followed by emission of the light at a characteristic color visually detectable with a light microscope. As in the EIA, the fluorescent labeled antibody is allowed to bind to the first antibody-hapten complex. After washing off the unbound reagent, the remaining ternary complex is then exposed to the light of the appropriate wavelength, the fluorescence observed indicates the presence of the hapten of interest. Immunofluorescence and EIA techniques are both very well established in the art and are particularly preferred for the present method. However, other reporter molecules, such as radioisotope, chemiluminescent or bioluminsecent molecules, may also be employed. It will be readily apparent to the skilled technician how to vary the procedure to suit the required purpose. It will also be apparent that the foregoing can be used to detect directly or indirectly (i.e., via antibodies) the P40 of this invention.

Accordingly, the present invention is also directed to a kit for the rapid and convenient assay of P40 in mammalian body fluids (e.g. serum, tissue extracts, tissue fluids), in vitro cell culture supernatants, and cell lysates. The kit is compartmentalized to receive a first container adapted to contain an antibody to P40, or to an antigenic component thereof, and a second container-adapted to contain a second antibody to P40, or to an antigenic component thereof, said second antibody being labeled with a reporter molecule capable of giving a detectable signal as hereinbefore described. If the reporter molecule is an enzyme, then a third container adapted to contain a substrate for said enzyme is provided. In an exemplified use of the subject kit, a sample to be tested for P40 is contacted with the contents of the first container for a time and under conditions for P40, if present, to bind to the antibodies contained in said first container. After removal of unbound material (e.g. by washing with sterile phosphate buffered saline), the secondary complex is contacted with the contents of the second container. If the antibodies of the first container have bound to P40, then the antibodies of the second container bind to the secondary complex to form a tertiary complex and, since said second antibodies are labeled with a reporter molecule, when subjected to a detecting means, the tertiary complex is detected.

Another aspect of this invention relates to a recombinant nucleic acid or an isolated nucleic acid molecule, said molecule defined herein to be DNA or RNA, encoding P40 or parts thereof. In one embodiment the recombinant nucleic acid molecule is complementary DNA (cDNA). It is considered within the scope of the present invention to include the cDNA molecule encoding mammalian P40, preferable murine and human P40, or to regions or parts thereof including any base deletion, insertion or substitution or any other alteration with respect to nucleotide sequence or chemical composition (e.g. methylation and glycosylation). Additionally, the present invention is directed to restriction fragments and synthetic fragments from a nucleic acid encoding mammalian P40. P40 encoded by cDNA or a recombinant DNA is referred to herein as recombinant P40. Moreover, another embodiment of this invention is directed to the genomic P40 gene, which may include recombinant clones like cosmids encoding the entire gene or subclones encoding exons, introns or any region of the mammalian P40 gene. Recombinant DNA encoding such subregions of the gene are useful as hybridization probes to detect the presence of P40 genes.

Methods considered useful in obtaining recombinant P40 cDNA are contained in Maniatis et al., 1982, in Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, New York, pp. 1-545, for example, or any of the myriads of laboratory manuals on recombinant DNA technology which are widely available. Briefly, polyadenylated mRNA is obtained from stimulated helper T cells and fractionated on agarose gels. Optionally, aliquots of mRNA can be injected into Xenopus laevis oocytes for translation and assayed for P40 activity using the methods contained herein to enriched fractions of mRNA translating into P40 active molecules. Alternatively, mRNA not enriched is used as template for cDNA synthesis. Libraries of cDNA clones are constructed in the Pstl site of the vector pBR322 (using homopolymer tailing) or in a variety of other vectors (e.g. the Okayama-Berg cDNA cloning vectors, Messing cDNA cloning vectors and the like). Specific cDNA molecules in a vector in said library are then selected by using specific oligonucleotides designed, based on amino acid sequences contained within P40, to encode at least part of said sequence. Particularly useful is the internal, partial amino acid sequence of murine P40 obtained after cyanogen bromide treatment which comprises: ##STR1## Olignucleotide sequences based on the foregoing amino acid sequence are particularly useful in identifying cDNA clones encoding P40 or its derivatives. Thus, poly(A)⁺ RNA can be prepared from the murine helper T cell line TUC7.51 after 24 hours stimulation with Concanavalin A (Con A) and used as a template for cDNA synthesis. The cDNA can be cloned into BamHI site of a pUC8 vector, transformed into E. coli and screened using a 64-fold degenerate probe corresponding to the amino acid sequence FQKTEMQ and subsequently with a 128-fold degenerate probe corresponding to the amino acid sequence ENLKDDP (See Example 9 for the exact sequence of the probes). The resulting positive clones are useful to isolate other mammalian genomic P40 genes and cDNAs. For example, the murine cDNA clone is used to screen a human genomic library, or other mammalian genomic library, to identify either the entire genomic gene or at least an exon thereof. If only a portion of the gene is isolated by this method, the remainder of the gene can be isolated by "chromosomal walking" with the new clone. Further, a genomic clone is particularly useful to isolate a cDNA clone and vice versa, especially from the same species. Thus, the murine cDNA clones can be used to isolate the murine genomic P40 gene.

The cDNA sequence encoding murine P40 is set forth below with the corresponding amino acid sequence: ##STR2##

The cDNA sequence with the corresponding amino acid sequence of human P40 is set forth below: ##STR3##

Once identified, cDNAs or recombinant DNAs encoding all or part of recombinant P40 are ligated into expression vectors. Additional genetic manipulation is routinely carried out to maximize expression of the cDNA in the particular host employed. Accordingly, P40 may be synthesized in vitro by inserting said cDNA sequence into a replicable expression vector, transforming the resulting recombinant molecule into a suitable host and then culturing or growing the transformed host under conditions requisite for the synthesis of the molecule. The recombinant molecule defined herein should comprise a nucleic acid sequence encoding a desired polypeptide inserted downstream of a promoter, a eukaryotic or prokaryotic replicon and a selectable marker such as resistance to an antibiotic.

A promoter consists of a specific nucleic acid sequence that is operably linked to the DNA encoding the desired polypeptide which is capable of effecting expression of said polypeptide. Likewise, the promoter can be replaced or augmented by any other genetic elements capable of effecting gene expression, including such elements as enhancers, transcription terminators, poly(A) signals and the like. The latter three elements are not always necessary and their use will depend on both the vector and host system used for gene expression. The need for any of these elements can be easily determined by one skilled in the art. Promoters are DNA sequence elements for controlling gene expression, in particular, they specify transcription initiation sites. Prokaryotic promoters that are useful include the lac promoter, the trp promoter, the P_(L) and P_(R) promoters of lambda and the T7 polymerase promoter. Eukaryotic promoters are especially useful in the invention and include promoters of viral origin, such as the SV40 late promoter and the Molony Leukemia Virus LTR, yeast promoters and any promoters or variations of promoters designed to control gene expression, including genetically-engineered promoters. Control of gene expression includes the ability to regulate a gene both positively and negatively (i.e., turning gene expression on or off) to obtain the desired level of expression.

One skilled in the art has available many choices or replicable expression vector, compatible hosts and well-known methods for making and using the vectors. Recombinant DNA methods are found in any of the myriad of standard laboratory manuals on genetic engineering.

The recombinant molecule may also require a signal sequence to facilitate transport of the synthesized polypeptide to the extracellular environment. Alternatively, the polypeptide may be retrieved by first lysing the host cell by a variety of techniques such as sonication, pressure dissintegration or toluene treatment. Hosts contemplated in accordance with the present ivention can be selected from the group comprising prokaryotes (e.g., Escherichia coli, Bacillus, sp., Pseudomonas sp.) and eukaryotes (e.g., mammalian cells, yeast and fungal cultures, insect cells and plant cultures). The artisan will also recognize that a given amino acid sequence can undergo deletions, substitutions and additions of nucleotides or triplet nucleotides (codons). Such variations are all considered within the scope of the present invention and may be prepared by site-directed mutagenesis techniques. Additionally, depending on the host expression recombinant P40, said P40 may or may not be glycosylated. Generally, eukaryotic cells, for example mammalian T cells and the like, provide glycosylated, recombinant P40. Prokaryotic cells, for example bacteria such as Escherichia coli and the like, do not glycosylate proteins. Hence, both glycosylated and non-glycoslated recombinant P40 are encompassed by the present invention.

Yet another aspect of the present invention provides transformant microoganisms and cultured cells containing the instant expression-vectors. Transformant microorganisms and cultured cells are made by introducing the replicable expression vector encoding mammalian P40, a derivative or a fragment thereof, into the desired cell or microorganisms by transformation, transfection or infection or virus or bacteriophage particles. Processes for transformation are well-known in the art and include, but are not limited to CaCl₂ treatment and electroporation for bacterial cells and CaPO₄ co-precipitation, protoplast fusion and electroporation for eukaryotic cells. Direct infection can be used when the vectors are viruses or bacteriophages. The detailed methods for these techniques can be found in standard laboratory manuals on recombinant DNA technology. The invention further contemplates any method for incorporating DNA into a host organism.

Another aspect of the present invention relates to the helper T cell lines which produce P40. As defined herein, P40 or compositions comprising same, stimulate the development of permanent antigen-independent T helper cell lines which are maintained by subcultivation every 3 to 4 days in medium with P40. Even more particularly, the present invention is directed to TS1, one of the factor-dependent cell lines derived from TUC2.15.

The following examples further illustrate the present invention.

EXAMPLE 1 Materials and Methods

Medium

Dulbecco's modified Eagle's medium supplemented with 10% (v/v) fetal bovine serum (FCS), 50 uM β-mercaptoethanol, 0.55 mM L-arginine, 0.24 mM L-asparagine and 1.25 mM L-glutamine are used for most cell lines except for 7TD1 and BCL1 which are grown in Iscove's medium.

T Cell Clones and Lines

Helper T cell lines are established and maintained in the absence of exogenous growth factors as described by Van Snick et al., Proc. Natl. Acad. Sci. USA 83:9679-9683, 1986. Lines TUC2 and TUC7 are derived from C57BL/6 mice immunized with keyhole limpet hemocyanin. Line TUC5 is obtained from the same strain of mice but after immunization with human transferrin. TUC13 is an allospecific BALB/c anti-C57B/6 line. Individual clones are derived from these lines by limiting dilution in the presence of 10% (v/v) medium conditioned by rat spleen cells stimulated with concanavalin A, and are denoted TUCx.y (where x stands for the number of the line and y for the number of the clone). These clones are subsequently expanded and maintained without exogenous growth factors like the parental cell lines. Cytolytic T cell clones of DBA/2 origin directed against syngeneic P815 mastocytoma are maintained with 50% (v/v) mixed lymphocyte culture medium as described by Maryanski et al., Eur. J. Immunol. 12:401-406, 1982. For use in growth factor assays, the T cells are separated from feeder cells by centrifugation over a layer of Lymphoprep (Nycomed AS, Oslo, Norway) washed and incubated at 5×10⁴ cells/well. Proliferations are measured on day 3 after a 6 hr pulse with methyl-labeled [³ H]-thymidine (0.5 uCi/well).

Preparation of Helper T Cell Supernatants

TUC2.15 and TUC7.51 cells, obtained from cultures stimulated 2 weeks earlier with antigen and feeder cells, are adjusted to 2×10⁶ cells/ml and incubated for 2-3 days in medium containing 0.5% (v/v) FCS and concanavalin A (ConA, 5 ug/ml). Supernatants (SN) are collected by centrifugation at 10,000 g for 20 min. When used for culture, crude SN are supplemented with 0.1M methyl-α-D-mannoside.

TS1 Growth Factor Assay

Factor-dependent TS1 cells are cultured in 1% (v/v) TUC2.15 SN. Before use in the growth factor assay, the cells are washed free of SN and cultured at a density of 3×10³ cells/well in 200 ul with serial dilutions of samples to be tested. After 3 days, cell growth is measured by colorimetric determination of hexosaminidase levels according to Landegren, J. Immunol. Methods 67:379-388, 1984. The dilution giving half-maximal absorbance at 405 nm is arbitrarily assigned one U/ml of activity.

Other Cell Lines

CTLL-2 (Gillis et al., J. Immunol. 120:2027-2032, 1978) is grown with 100 U/ml of human recombinant IL-2 DA-1 (Ihle et al., Adv. Viral Oncol. 4:95-137, 1984), Ea3.15 (Palacios et al., J. Exp. Med. 152:1036-1047, 1980) with 10% (v/v) WEHI-3 SN as a source of IL3 and 7TD1 with a 1/500 dilution of TUC2.15 SN as a source of IL6 (Van Snick et al. supra). Assays using these cell lines are carried out as described for the TS1 line and proliferations are measured either by hexosaminidase determinations or by thymidine incorporation. In vivo passaged BCLI cells (Slavin et al., Nature 272:624-626, 1978) are frozen in aliquots and thawed just before use. Proliferation of BCL1 is measured by thymidine incorporation in 7 day-old cultures seeded with 10⁴ cells/well.

Cytokines and Growth Factors

Purified natural human IL1β (Van Damme et al., Nature 314:266-268, 1985), recombinant human IL2 (Devos et al., Nucleic Acids Res. 11:4307-4323) and purified murine IL3 (Ihle et al., J. Immunol. 129:2431-2436, 1982) are as described. Human recombinant granulocyte colony-stimulating factor (G-CSF) and mouse recombinant granulocyte-macrophage colony stimulating factor (GM-CSF) is described by DeLamarter et al., EMBO J. 4:2575-2581, 1985. Platelet-derived growth factor (PDGF) is described by Heldin et al., Proc. Natl. Acad. Sci. USA 76:3722-3726, 1979. Epidermal growth factor (EGF) is purchased from Boehringer Mannheim (Fed. Rep. Germany). Mouse IL4, IL5 and IL6 are purified as described by Van Snick, supra, and Vink et al., Eur. J. Immunol. 18: 607-612, 1988.

Antibodies

Anti-IL4 antibody 11B11 (Ohara et al., Nature 315:333-336, 1985) and anti-IL2 receptor antibody 5A2 (Moreau et al., Eur. J. Immunol. 17:929-935, 1987) are as described.

Purification of TS1 Growth Factor

Adsorption to silicic acid and gel filtration is performed as described (Van Snick Supra). Active fractions from the gel filtration column are pooled, concentrated by ultrafiltration on an Amicon YM-10 membrane in the presence of 10⁻⁴ (v/v) dilution of Tween 20 and transferred to 1M Na₂ SO₄ buffered to pH 7.0 with 0.1M sodium phosphate before injection onto a TSK-Phenyl column (LKB, Bromma, Sweden) equilibrated in the same buffer. After a 10 min wash in the starting buffer, elution is carried out at 0.6 ml/min with a linear gradient of a 1:1 mixture of a sodium phosphate buffer (0.1M, pH 7.0) and ethylene glycol. Active fractions are further fractionated on a MonoQ column (Pharmacia Fine Chemicals, Uppsala, Sweden) equilibrated in 20 mM ethanolamine-HCl pH 9.5, 20 mM NaCl and 10⁻⁴ (v/v) Tween 20. The column is developed at 0.8 ml/min with a 30 min linear gradient of NaCl (8 mM/min). Pooled active fractions are concentrated and adjusted to contain 0.05% (w/v) trifluoroacetic acid (TFA) before injection on a Cl 25-nm pore-size TSK TMS-250 HPLC column (LKB). The column is developed for the first 10 min with a linear gradient from 0 to 35% (w/v) acetonitrile in 0.05% (w/v) TFA, which is followed by a shallow 35-36% gradient for the next 60 min. Flow rate is adjusted to 0.8 ml/min; 1 min fractions are collected in Eppendorf tubes containing 10 ul of 1M NH₄ HCO₃ and 5 ul of Tween 20 (1% (v/v) in water) and lyophilised. Total protein is measured fluorometrically with benzoxanthene following Neuhoff et al., Hoppe-Seyler's Z. Physiol. Chem. 360:1657-1670, 1979. The purity of the final product is assessed by NaDodSO₄ /PAGE in 12% (w/v) acrylamide gels. Isoelectric focusing is performed with a LKB (Bromma, Sweden) vertical gel apparatus. Material is recovered from gels by overnight incubation in 130 mM NaCl containing Tween 20 (10⁻⁴ v/v) and 10 mM sodium phosphate, pH7.0. Affinity chromatography on lentil lectin-Sepharose is done following the procedure described by the manufacturer (Pharmacia, Uppsala, Sweden).

Amino Acid Sequence Analysis

Automated amino acid sequence analysis is performed with an Applied Biosystems sequencer (Model 477A) equipped with an on-line phenylthiohydanthoin amino acid analyzer (Model 120A). In situ cyanogen bromide cleavage of P40 (≈10 ug) is performed on the glass fiber sample disk of the gas-phase sequencer according to a procedure described by Simpson et al. Biochem. Internat. 8:787-791, 1984, hereinafter Simpson I. Sequence comparisons are made with the following databases: Protein Sequence database of PIR, National Biomedical Research Foundation (release 15.0, December 1987); Swiss-Prot Protein Sequence Data Bank version 5 (September 1987, compiled by A. Bairoch, University of Geneva, Medical Biochemistry Department, 1211 Geneva 4, Switzerland); G.B. trans Protein Data Base Release 1.0 (August 1987) compiled from GENBANK release 50.0 by J. Coventry, Walter and Eliza Hall Institute of Medical Research, Parkville 3050 Australia; and PG trans Protein Data Base release 38.0 (December 1985) GENBANK, Instit. Pasteur, Paris, France.

S1 Nuclease Protection Assay

The transcription sites of the human and murine P40 genes were determined by S1 nuclease mapping as described in Davis L. G. et al. (1988) Methods in molecular biology. Elsevier Science Publishing Co. Inc., New York. For the murine gene, a single-stranded probe, including 163 nucleotides, downstream from the initiator ATG and 421 bases of the 5' flanking region, was constructed using a 584 bp EcoRV/BanII fragment cloned in M13. Similarly, a human P40 probe was constructed using a 345 bp BglII/BamHI fragment containing the first 77 bp of the coding sequence and 268 bp of the 5' flanking region of the human P40 gene. These probes were hybridized with poly(A)⁺ RNA from a ConA-activated mouse helper T cell clone (TUC7.51) and from PHA-PMA stimulated human PBMC, respectively.

Southern blotting

Mouse high molecular weight DNA was isolated from T cell leukemia L1210 and from mastocytoma P815. Human DNA was from lymphoblastoid cell line CESS and from HeLa cells. DNAs were digested with restriction endonucleases and electrophoresed on a 0.8% agarose gel. Southern blots were hybridized with ³² P-labeled mouse (clone P40.2B4) or human (clone cH40.4) P40 cDNA.

Cellular preparations

Peripheral blood mononuclear cells (PBMC) were prepared by Lymphoprep (Nycomed AS, Oslo, Norway) density gradient centrifugation. T cells were separated by rosetting, using sheep red blood cells treated with aminoethylisothiouronium bromide (Sigma, St. Louis, Mo.). This procedure yielded populations that were 90% CD3⁺ as determined by flow cytometry. In some experiments, T cells were further enriched by nylon wool filtration prior to sorting of CD4⁺ and CD8⁺ cells by flow cytometry. The resulting preparations contained 92-94% CD4 ⁺ or CD8 ⁺ cells. Stimulations were performed for 24 hours in RPMI 1640 medium supplemented with 10% fetal calf serum. Phytohemagglutinin-P (Difco Laboratories, Inc., Detroit, Mich.) was added at 30 μg/ml, PMA at 3 ng/ml and ionophore A23187 at 10 ng/ml. Anti-CD3 antibody (OKT3) was used at 10 μg/ml, LPS (E. coli O55:B5, Difco) at 20 μg/ml and Staphylococcus aureus strain Cowan 1 (Calbiochem) at 10 μg/ml.

RNA analysis

Northern blots were prepared on nylon filters with 10 μg total RNA isolated as described [Glisin, V. et al. (1974) Biochemistry 13:2633] and fractionated by electrophoresis in 1.2% agarose gels with 6% formaldehyde. Gels were stained with ethidium bromide prior to transfer and the RNA content of each lane was verified after transfer by examining the filters under U.V. light. Hybridizations were carried out with ³² P-labeled cRNA probes essentially as described in Zinn, K. et al. (1983) Cell 34:865. Cytoplasmic RNA was extracted according to Maniatis et al. (1982), and denatured with formaldehyde before blotting onto nitrocellulose filters. Hybridizations were performed as described [Van Snick, J. et al. (1988) Eur. J. Immunol. 18:193] with a ³² P-labeled human P40 cDNA and with a chicken β-actin probe as a control.

EXAMPLE 2 Detection of T Cell Growth Factory Activity

TUC2.15 is a C57B1/6 helper T cell line that requires antigen and antigen-presenting cells for long term growth in vitro. In an attempt to grow these cells without feeders and antigens it is surprisingly discovered that, after supplementing the culture medium with 10% (v/v) autologous supernatant (SN) obtained after stimulation with ConA, this SN is able to induce cell proliferation without further requirement for antigen or feeder cells. This growth factor activity is not inhibited by either anti-IL4 or anti-IL2 receptor antibodies (Table 1), indicating that the activity is mediated neither directly or indirectly by these molecules.

In addition to its activity in short term proliferations, the SN also readily stimulates the development of permanent antigen-independent cell lines, which are maintained by subcultivation every 3-4 days in medium supplemented with 1% (v/v) SN (FIG. 1). Attempts to derive antigen-independent cell lines with IL2 in this manner are to date unsuccessful. A second helper T cell clone, TUC7.51 also gives rise to an antigen-independet cell line upon culture in autologous SN. The factors active on the two cell lines are apparently identical, since TUC7.51 SN supported the growth of TUC2.15 cells and vice versa.

TS1, one of the factor-dependent cell lines derived from TUC2.15 is selected for further identification of the growth factor. This choice is based on the observation that TS1 grows quickly, with a doubling time of 11 h, and responds to very small concentrations of SN, half-maximal proliferation being obtained at dilutions between 10⁻⁵ and 10⁻⁴ (v/v). To determine the specificity of the TS1 assay, cells are incubated with a variety of purified growth factors or crude SN and found that only IL4 and TUC2.15 SN support TS1 growth (Table 2). Since anti-IL4 antibodies fail to inhibit the effects of TUC2.15 SN, the aforementioned activity is a new T cell growth factor.

                  TABLE 1                                                          ______________________________________                                         Proliferation of TUC2.15 Helper T Cells Induced by Autologous                  Supernatant (SN); Independence from IL2 and IL4                                           Proliferation in response to                                        Antibodies Added                                                                            IL2       IL4    TUC2.15 SN                                       ______________________________________                                                    (kepm)                                                              none         152       18     37                                               anti-IL2 receptor                                                                           4         16     32                                               anti-IL4     156       1      33                                               ______________________________________                                          TUC2.15 helper T cells (5 × 10.sup.4 /well) are incubated for 3 day      with IL2 (100 U/ml), IL4 (100 U/ml) or TUC2.15 SN (1% v/v) in the presenc      of antiIL2 receptor antibody 5A2 (30 ug/ml) or antiIL4 antibody 11B11 (10      ug/ml). Thymidine incorporation is measured on day 3.                    

                  TABLE 2                                                          ______________________________________                                         Growth of TS1 in Response to Various Cytokines                                 Factors      Dose/Dilution                                                                              Cell Growth (A.sup.405)                               ______________________________________                                         TUC2.15 SN   1/12.500    1.96                                                  IL1          100 U/ml    0                                                     IL2          100 U/ml    0                                                     IL3          100 U/ml    0.01                                                  IL4          100 U/ml    1.36                                                  IL5          100 U/ml    0                                                     IL6          20 ng/ml    0                                                     GM-CSF       10 ng/ml    0                                                     G-CSF        4 ng/ml     0                                                     M-CSF (crude)                                                                               1/4         0.02                                                  EGF          50 ng/ml    0                                                     PDGF         4 ug/ml     0.02                                                  ______________________________________                                          TS1 cells are incubated for 3 days in the presence in various factors or       SN. All reagents are tested over a 100fold range but results are given fo      the highest dose only. None of the factors that score negatively at the        highest dose have any effect at lower dose. Cell growth is measured by         colorimetric determination of hexosaminidase levels. Absorbance (A) of         cultures at 405 nm incubated without growth factors ranges from about 0.1      to about 0.15 and is subtracted.                                         

EXAMPLE 3 Purification of the T Cell Growth Factor

Large batches of T cell SN are produced by stimulating TUC2.15 and TUC7.51 cells with ConA as described in Example 1. The active material is concentrated by adsorption to silicic acid and applied to an Ultrogel AcA54 gel filtration column. The major growth promoting activity, which is destroyed by trypsin, elutes as a symmetrical peak in the 30-40 kDa region (FIG. 2A), and is therefore designated P40. Subsequent experiments are carried out with TUC7.51 SN because the concentrations of P40 are higher in this material.

Preliminary characterization of the growth factor indicates that it has a pI of ≈10 and is glycosylated, 60% of the activity being retained on a lentil lectin column. Based in part on this information, the following purification protocol is adopted. Active fractions from the gel filtration step are further separated by hydrophobic interaction chromatography on a TSK-phenyl column (FIG. 2B) followed by passage through a MonoQ anion exchange column equilibrated at pH 9.5. At this elevated pH, most contaminants are retained on the column, whereas P40 elutes mainly in the flow-through fractions, as expected from its high pI (FIG. 2C). Final purification is achieved by reversed phase chromatography on a Cl-column equilihbrated with 0.05% (w/v) TFA. P40 is recovered in a single peak eluting at an acetonitrile concentration of 35% (v/v) (FIG. 2D). At the end of this purification, P40 stimulates half-maximal growth of TS1 at a concentration of ≈5 pg/ml (FIG. 3), which corresponds to a 2000-fold purification. On average, the overall yield ranges from about 5 to about 10%.

The purified protein is very heterogeneous with a Mr of about 32 to about 39 kDa in NaDodSO₄ /PAGE both under reducing (FIG. 4) and non-reducing conditions. Biological activity is recovered from the corresponding fractions of a non-reduced gel, but exposure to NaDodSO₄ and 2-mercaptoethanol destroys most of the activity.

EXAMPLE 4 Amino Acid Sequence Analysis of Murine P40

Edman degradation of P40 (≈250 pmol) did not yield N-terminal sequence. For sequence analysis, P40 (immobilized on the polybrene-treated sample disk of the sequencer) is acylated (Tarr, Methods of Protein Microcharacterization [ed. J. E. Shively] Human Press, pp. 155-194, 1986) and then subjected to in situ cyanogen bromide treatment as described by Simpson I. Sequence analysis is then continued and yields the following major amino acid sequence (110 pmol): NH₂ -Ala Gly Asn Thr Leu Ser Phe Leu Lys Ser Leu Leu Gly Thr Phe Gln Lys Thr Glu.

This internal sequence show no significant similarity with that of other proteins stored in the data bases listed in Example 1.

The determination of the complete amino acid sequence was achieved by chemical methods.

Briefly, before proteolytic digestion native P40 was reduced with dithiothreitol and carboxymethylated with iodoacetic acid to yield Cm-P40. Peptides (indicated in FIG. 7) were prepared for sequence analysis by cleavage of Cm-P40 with endoproteinase, Asp-N, trypsin, chymotrypsin, and cyanogen bromide (denoted by D, T, C, and N, respectively in FIG. 7). Subpeptides of the endoproteinase Asp-N were derived by cleavage with Staphylococcus aureus V8 protease (denoted with hyphenated S suffixes). In FIG. 7, amino acid residues not identified are indicated by X.

The exact methodology of amino acid sequence determination is described below:

A. Materials

Tween 20, guanidine hydrochloride (Sequenal grade) and trifluoroacetic acid (F₃ AcOH; 99+% pure grade) were purchased from Pierce Chemical Co. (Rockford, Ill., USA). Iodoacetic acid (puriss grade) was obtained from Fluka (Buchs, Switzerland) and was recrystallized prior to use. Dithiothreitol was from Calbiochem (La Jolla, Calif., USA). Sodium chloride (Aristar grade) and acetic anhydride were purchased from BDH (Poole, UK). Cyanogen bromide (Univar grade) was from Ajax Chemical Co. (Sydney, Australia). All other chemicals were of the highest grade commercially available.

Trypsin (treated with tosylphenylethylchloromethane) and chymotrypsin were purchased from Worthington Biochemical Co. (New Jersey, USA). Staphylococcus aureus strain V8 protease was obtained from Miles Co. (Napperville, Ill., USA). Endoproteinase AspN from a Pseudomonas fragi mutant and N-glycanase F were obtained from Boehringer Mannheim GmbH (West Germany). All organic solvents were HPLC grade (Chromar grade, Mallinckrodt, Kentucky, USA). Deionized water, obtained from a tandem Milli-RO and Milli-Q system (Millipore, Inc., Massachusetts, USA) was used for all buffers.

B. Preparation of murine S-carboxymethyl-P40 (Cm-P40)

P40 (15 ug in 120 ul 35% aqueous acetonitrile containing 0.1% (v/v) F₃ AcOH and 0.02% Tween 20 was concentrated to approximately 10 ul by centrifugal centrifugation (Savant, Ind. Hicksville, N.Y.), diluted to 160 ul with 7.5M guanidine.HCL containing 0.2M Tris.HCl buffer, pH 8.5, 0.002M EDTA and 0.02% (v/v) Tween 20 and then reduced with dithiothreitol (0.015M) at 40° C. for 4.5 h. Alkylation was achieved by the addition of iodacetic acid (final concentration, 0.05M) to the mixture and incubation continued for 30 min at 25° C. in the dark. The reaction was halted by addition of 25 ul of 2-mercaptoethanol. Cm-P40 was recovered from the mixture using a reversed-phase high-performance liquid chromatography (RP-HPLC) procedure previously described (Simpson et al., Eur J. Biochem. 1176:187-107, 1988, hereinafter Simpson II). The Cm-P40-containing fraction (60 ul) was adjusted to 0.02% (v/v) with respect to Tween 20 and then diluted to 1 ml with an appropriate buffer (containing 0.02% (v/v) Tween 20) prior to enzymatic digestion.

C. Trypsin digestion

Cm-P40 (7 ug) in 1 ml of 1% (w/v) NH₄ HCO₃, pH 7.8 containing 0.001M CaCl₂ and 0.02% (v/v) Tween 20 was digested with 0.5 ug trypsin for 16 h at 37° C.

D. Chymotrypsin digestion

Cm-P40 (6 ug) in 1 ml of 1% (w/v) NH₄ HCO₃, pH 7.8 and 0.02% (v/v) Tween 20 was digested with 0.6 ug chymotrypsin for 16 h at 37° C.

E. Endoproteinase Asp-N digestion

Cm-P40 (15 ug) in 1020 ul of 0.05M sodium phosphate buffer, pH 8.1, 0.02% (v/v) Tween 20 was digested with 0.7 ug of freshly prepared endoproteinase Asp-N for 16 h at 34° C.

F. Staphylococcus aureus strain V8 protease digestion

Endoproteinase Asp-N peptide D3 in 1 ml of 1% (w/v) NH₄ HCO₃, 0.02% (v/v) Tween 20 was digested with 0.5 ug S. aureus V8 protease at an enzyme/substrate ratio of 1:10 for 16 h at 30° C.

G. Purification of polypeptides by high-performance liquid chromatography instrumentation

Peptide mixtures resulting from enzymatic cleavages were fractionated by reversed-phase HPLC on a Hewlett-Packard liquid chromatograph (model 1090A) fitted with a diode-array detector (model 1040A) as described (Simpson II).

H. Column Supports

The following columns were used for the purification of Cm-P40 and derived peptides: (a) Brownlee RP-300 (300 nm pore size, 7-um particle diameter, octylsilica packed into a stainless steel column 30×2.1 mm i.d. or 50×1 mm i.d. (Brownlee Laboratories, Santa Clara, Calif. USA). (b) Dimethylaminoazobenzene sulfonyl chloride (DABS-C1) amino acids were separated and quantitated on a Brownlee PTC amino acid analysis column (220×2.0 mm i.d.) (Applied Biosystems, Foster City, Calif., USA).

I. Peptide nomenclature

The following prefixes are used to denote the origin of various peptides: T, Trypsin; CN cyanogen bromide; C, chymotrypsin; D, endoproteinase Asp-N. Peptides resulting from sub-digestion of endoproteinase Asp-N peptides with S. aureus V8 protease are denoted by hyphenated S suffixes. Peptides are numbered in the order of their positions in the final sequence.

J. Cyaogen bromide cleavage

After P40 (10 ug) was subjected to several cycles of Edman degradation in the protein sequencer without any detectable PTH-amino acids, the sequence analysis was stopped. In situ cyanogen bromide cleavage of native P40 was performed on the glass fiber sample disk of the protein sequencer according to a procedure previously described (Simpson, I). Sequencer background levels which had arisen during the sequence analysis were reduced by treating the sample disk with 30 ul aqueous 50% (v/v) N-ethylmorpholine followed by 10 ul acetic anhydride (60 min at 25° C.). The filter was vacuum dried and then treated with at 20-fold excess of cyanogen bromide in 70% (v/v) formic acid for 15 h at 25° C. At the end of this time the sample filter was vacuum dried for 30 min and the sequence analysis continued.

K. Amino acid sequence analysis

Automated Edman degradation of protein and peptide was performed using Applied Biosystems sequencers (models 470A and 477A) equipped with on-line phenylthiohydantoin (Pth) amino acid analyzer (model 120A). Total Pth-amino acid derivatives from the sequencer were injected onto the liquid chromatograph using a modified sample transfer device as described [Begg, et al., in "Techniques in Protein Chemistry", (Hugli, T. E., Ed.) Academic Press, Orlando Fla., USA, in press]. Polybrene was used as a carrier.

EXAMPLE 5 Peptide purification by microbore RP-HPLC

Cm-P40 (15 ug) was digested with endoproteinase Asp-N and the digest fractionated by RP-HPLC on a short microbore column (30×2.1 mm i.d.), employing a low-pH (F₃ AcOH, pH 2.1) mobile phase and a gradient of acetonitrile. Three major peptide-containing peaks were detected: D1, D2 and D3 (FIG. 8). Spectral analyses of these peptides were performed using real-time photodiode-array spectroscopy and the absorption spectra of peptides D1, D2 and D3 are shown in FIG. 9. The high absorbance at 290 nm of peptide D1 is indicative of the presence of a tryptophan residue. The D2 and D3 peptides have high absorbance at 280 nm and low absorbance at 290 nm which is characteristic of tyrosine-containing peptides. The presence of tryptophan residue in peptide D1 is supported by the derivative absorbance spectrum shown in FIG. 10. Enhancement of resolution by second-order-derivative spectroscopy reveals extrema at 290; 2 nm and 280±2 nm which are characteristic of tryptophan residues. Peptide D3 was subdigested with S. aureus V8 protease and the resultant digest fractionated by RP-HPLC at low pH (F₃ AcOH) (FIG. 11A).

Reversed-phase HPLC purification of peptides resulting from treatment of Cm-P40 with chymotrypsin and trypsin were performed and analyzed in a similar manner. Reversed-phase fractionation of these digests, however, resulted in a complex pattern of peptide-containing peaks (FIGS. 11B and 11C). All of the peptide fractions from the first dimension RP-HPLC were subjected to a second chromatographic step using the same chromatographic support and acetonitrile gradient but a different mobile phase (e.g., unbuffered sodium chloride or 20 mM sodium phosphate, pH 7.0). For some peptides a third chromatographic step was necessary before a homogeneous peptide could be isolated. In the latter situation, an ODS-hypersil column and a different organic solvent (methanol) were used for the chromatography (Simpson II).

EXAMPLE 6 Characterization of glycosylation state of P40

Cm-P40 (0.5 ug) was iodinated using the iodine monochloride procedure. ¹²⁵ I-Cm-P40 was separated from free ¹²⁵ I by sequential gel filtration and cation-exchange chromatography. ¹²⁵ I-Cm-P40, untreated, reduced with 2-mercaptoethanol for 5 min at 95° C., or digested with N-glycanase F (Genzyme, Boston, Mass., USA) or endo-α-N-acetylgalactosaminidase (O-glycan-peptide hydrolase, Boehringer Mannheim) for 16 h at 37° C. according to the manufacturer's instructions was electrophoresed on a 10-15% gradient polyacrylamide gel in the presence of SDS. The gel was stained with Coomassie Blue R250 using the Phast electrophoresis system (Pharmacia, Uppsala, Sweden) according to the manufacturer's instructions. ¹²⁵ I-Cm-P40 was detected by autoradiography using Hyperfilm, MP (Amersham, Buckinghamshire, UK).

Purified iodinated P40 electrophoresed as a single broad band of apparent M_(r) 32,000-39,000 daltons on 12% SDS-PAGE in both the unreduced and reduced (2-mercaptoethanol) state (see FIG. 4, Lane 1 and 4) indicating that it is a monomeric protein. Endo-α-N-acetylgalactosaminidase (O-glycanase) treatment of P40 had no apparent effect on the molecular mass (FIG. 4, Lane 3) but treatment with N-glycanase F caused a reduction in apparent M_(r) to 15,000-16,000 Da (FIG. 4, Lane 2). The lack of effect of O-glycanase indicates that P40 does not contain O-linked carbohydrate chains or that these sites are not accessible in the intact molecule. Since N-glycanase F releases carbohydrate moieties attached to asparagine residues (N-linked) this indicates that P40 consists of a protein core (M_(r) 15,000-16,000) with considerable amounts of N-linked sugars.

Murine P40 has 126 amino acids. The calculated M_(r) from the sequence analysis is 14,150. The difference in the calculated M_(r) and the measured M_(r) for native P40 (32-39 kDa) can be attributed to N-glycosylation since upon treatment with N-glycanase F the M_(r) is reduced to 15,000-16,000 (FIG. 4). The protein sequence data provides information on the post-translational processing of mature P40. For instance, since no amino acid was identified at positions 32, 60, 83 and 96 (FIG. 10) and since these positions meet the criteria for N-linked glycosylation sites (i.e. Asn-Xaa-Thr/Ser), these data are consistent with asparagines being glycosylated at these four positions. Confirmation of asparagine residues at positions 32, 60, 83 and 96 and the COOH--terminal residue (P40-126) was provided by sequence analysis of a P40 cDNA clone.

EXAMPLE 7 Analysis of N-terminal block in murine P40

The exact nature of the blocked N-terminus was determined by a combination of amino acid analysis, fast-atom-bombardment mass spectrometry, and peptide synthesis. These analyses indicated the N-terminus of murine P40 is likely to be pyroglutamic acid.

The methods involved in determining the amino terminal residue of P40 and a discussion thereof follow:

Method

A. Amino acid analysis

Amino acid analysis was performed on a Beckman amino acid analyzer (model 6300) equipped with a model 7000 data system or by using the dimethylaminoazobenzene sulfonyl chloride (DABS-Cl) precolumn derivatization procedure using microbore column RP-HPLC (Simpson, et al., Euro. J. Biochem. 153: 629-637, 1985). Samples were hydrolyzed in vacuo at 110° C. for 24 h with gaseous HCl generated from 6M HCl containing 0.1% (w/v) phenol.

B. Fast-atom-bombardment mass spectrometry

Fast-atom-bombardment mass spectrometry (Barber et al., Anal. Chem., 54: 645A-657A, 1982) was performed using a VG 70/70E-HF forward-geometry double-focussing mass spectrometer (VG Analytical, Manchester, UK) equipped with an Ion Tech saddle-field fast-atom gun. Sample was applied in 2 ul of 0.1% (v/v) aqueous F₃ AcOH to the sample stage containing 1 ul of pre-applied mixture of dithiothreitol/dithioerythritol (5:1). Xenon atoms at a potential of 8 keV and a discharge potential of 1 mA were used for sample bombardment. Scans were performed at 40s/decade at a resolution of 1500. Positive-ion spectra were acquired by multi-channel analysis mode using a VG 11/250J data system.

C. Peptide synthesis

Fluorenylmethoxycarbonyl (Fmoc)-polyamide solid phase peptide chemistry was employed to synthesize two peptides corresponding to the N-terminal decapeptide of P40 (endoproteinase Asp-N peptide D1) with either glutamic acid or glutamine as the amino terminal residue. The conventional Fmoc polyamide side chain protecting groups were employed: Trp (CHO); Arg (Mtr), Mtr=4-methoxy- 2,3,6,-trimethylbenzenesulfonyl); Glu (OtBu); Cys (tBu). Pentafluorophenyl (OPfp) esters of all Fmoc-amino acids in dimethylformamide with the exception of Fmoc-Arg (MtC) which was activated as an 1-hydroxybenzotriazole (HOBt) ester, were employed for sequential coupling of activated amino acids on RAMPS (DuPont, N.J.) Wang resin. Peptide bond formation was generally complete within 120 min provided that the concentration of the OPfp ester was 2.5×times greater than the concentration of derivatized resin and provided that one equivalent of 1-hydroxybenzotriazole was added to the coupling mixture in order to catalyze the reaction. Upon completion of the synthesis, the peptide was deprotected and cleaved from the resin by extended treatment with F₃ AcOH (containing 5.4% thioanisol, 0.6% 1,2-ethanedithiol). Crude synthetic peptides and their derivatives (e.g. S-carboxymethyl-peptides) were purified by reversed-phase HPLC. The pure synthetic peptides chromatographed as single peaks on reversed-phase HPLC (Brownlee RP-300 column 30×2.1 mm, i.d.) and gave the expected amino acid ratios.

Peptides (30 ug in 100 ul 0.1% F₃ AcOH) were acetylated with acetic anhydride by treatment with 6 ul N-ethylmorpholine (Pierce, sequenal grade) followed by 2 ul acetic anhydride (Fluka, puriss grade) for 10 min at 25° C. Formation of pyroglutamyl peptides was accomplished by treating the glutamine peptide at 110° C. for 16 h at pH 7.8 under nitrogen.

Discussion

Analysis of three major Asp-N peptides (D1-D3) and the S. aureus V8 protease subpeptides of D3 provided 65% of the P40 amino acid sequence. Of the three peptides, D1, the single tryptophan-containing peptide was N blocked, indicating that this peptide was derived from the N-terminal portion of the polypeptide chain. The amino acid composition of the N-blocked Asp-N peptide D1 was consistent with the tryptophan-containing tryptic peptide T1 with the N-terminal addition of two extra residues (Glx and Arg).

Fast-atom-bombardment mass spectrometry (FAB-MS) of Asp-N peptide D1 revealed a protonated molecular ion (MH⁺) of mass 1248 which only corresponds to the amino acid composition of this peptide if the blocking group was assumed to be pyroglutamic acid. The nature of the N-blocking group was examined using two synthetic decapeptides D1 with either glutamic acid or glutamine at the amino terminus (see FIGS. 7 and 12). As shown in FIG. 12, the endoproteinase Asp-N peptide D1 and the pyroglutamyl synthetic peptide co-chromatographed on reversed-phase HPLC (retention time, 20.50±-0.2 min) and were well resolved from the glutamyl synthetic peptide (retention time, 22.70±0.2 min). After acetylation, the chromatographic behavior of D1 and the pyroglutamyl synthetic peptide was identical (no increase in retention time) while the acetylated glutamyl synthetic peptide exhibited a marked increase in retention behavior (retention time was 28.97±0.2 min compared to the non-acetylated form, 22.70±0.2 min). The amino terminus of P40 is likely to be pyroglutamic acid since the amino-terminal endoproteinase Asp-N peptide D1 behaves in exactly the same manner as the synthetic pyroglutamyl peptide before and after acetylation on reversed-phase HPLC. FAB-MS of the glutamyl synthetic peptide yielded a molecular mass of 1248 which was in perfect agreement with that obtained for Asp-N peptide D1.

EXAMPLE 8 Biological Activity of Purified P40

Purified P40, at concentrations up to 20 ng/ml, did not support the proliferation of either IL3-dependent myeloid cell lines (FDCP-1, Ea3.15 and DA-1), IL5-dependent B cell lymphoma BCL1, or IL6-dependent B cell hybridoma 7TD1. Unlike IL2, and to some extent IL4, it also fails to stimulate any of six cytolytic T cell clones tested (Table 3). By contrast, strong proliferations are observed with some but not all helper T cell lines. Both IL2-producing (TH₁ type, TUC7.33) and IL4-producing (TH₂ type, e.g., TUC2.15) clones are found among the responders. A significant correlation, illustrated in Table 3 for clone TUC7.51, is observed between the time spent in culture and the responses to P40 and IL4.

                  TABLE 3                                                          ______________________________________                                         Comparison of the T Cell Growth Factor Activities                              of IL2, IL4, and Purified P40                                                                    Proliferation in                                                               response to.sup.a                                            T Cell Lines and Clones IL2       IL4  P40                                     ______________________________________                                         Cytolytic T Cells                                                                            CTLL-2    445       0.6  0.8                                                   P35:10    683       24   1.2                                                   P35:48    303       4    1.8                                                   P91:6     195       2    1.6                                                   P1:5      993       12   1.2                                                   P1:204-8  630       9    1.2                                     Helper T Cells                                                                               TUC2      311       2    14                                                    TUC2.15   1,806     813  240                                                   TUC5      263       20   13                                                    TUC5.37   253       4    0.8                                                   TUC7.33   115       276  235                                                   TUC7.51.sup.b                                                                            1,179     27   17                                                    TUC7.51.sup.c                                                                            1,345     634  199                                                   TUC13.1   116       51   1.7                                     ______________________________________                                          .sup.a Cells are incubated with or without the indicated growth factors        and thymidien incorporation is measured on day 3. Factor dosage is as          follows: 100 U/ml for IL2 and IL4, and 10.sup.3 -10.sup.4 U/ml for P40.        The results are shown as ratios of radioactivity incorporated with and         without factors.                                                               .sup.b 1 monthold culture                                                      .sup.c 1 yearold culture                                                 

EXAMPLE 9 Cloning and Characterization of the Murine P40 Gene

Screening of cDNA library

Double-stranded cDNA was prepared according to Gubler, et al., Gene 25: 263, 1983, using polyadenylated RNA isolated from P40-producing helper T cells TUC7.51 after a 24 h stimulation with ConA (2.5 ug/ml). The cDNA was cloned into the BamHI site of a pUC8 vector and transformed into E. Coli strain DH5. Transformants were screened by in situ hybridization with two end-labeled 20-mer oligonucleotide probes. For the initial screening, a 64-fold degenerate probe

[5'-TGCAT(C+T)TC(X)GT(C+T)TT(C+T)TG(G+A)AA-3'] corresponding to amino acid sequence FQKTEMQ (positions 114-120, see text) was used. Positive clones were subsequently tested with a 129-fold degenerate probe

[5'-GG(A+G)TC(A+G)TC(T+C)TT(X)AG(A+G)TT(C+T)TC-3'] corresponding to sequence ENLKDDP (positions 17-23, see text).

DNA sequencing

DNA was sequenced by the dideoxynucleotide procedure after subcloning into a M13 vector. Appropriate fragments were generated by digestion with Pstl and Ncol restriction endonucleases using the sequencing strategy shown in FIG. 5.

Characterization of cDNA and Construction of Expression Vectors

A cDNA library was prepared, in a pUC8 vector, from a helper T cell clone that produces large amounts of P40 after stimulation with ConA. This library was screened with two oligonucleotide probes synthesized on the basis of selected amino acid sequence data obtained by analysis of P40 peptides. Of 20,000 independent transformants, 112 hybridized with the two probes. Most of these clones contained cDNa inserts of about 500 bp. Using one of these cDNA's as a probe, a strong signal was obtained with a transcript of about 700 nucleotides in Northern blots of poly(A)⁺ RNA isolated from P40-producing helper T cell clone TUC7.51. Poly(A)⁺ RNA from P815 mastocytoma, which does not produce detectable P40 activity, gave no signal at all.

To establish that the selected clones contained authentic P40 cDNA, an expression vector was constructed. Insert P40.2B4 was cloned into BamHI site of plasmid pZIPneoSV(X)1 (Cepko, et al., Cell 37: 1053, 1984) and transfected into Clone-1d fibroblasts (Kit, et al., Exp. Cell. Res. 31: 297, 1963). Cell supernatants collected 48 h after transfection were tested for their growth factor activity on P40-dependent TS1 cells. As shown in FIG. 6, supernatants from cells transfected with P40.2B4 cDNA (closed symbols), but not from mock-transfected cells (open symbols), supported the growth of TS1. This result indicates that P40.2B4 cDNA presumably contains the entire coding region of P40.

The complete nucleotide sequence of the cDNA insert of clone P40.2B4 was determined, and is shown under "Detailed Description of the Invention". It consists of 554 nucleotides with a 5' untranslated sequence of 15 nucleotides, an open reading frame of 432 nucleotides and a 3' untranslated region of 107 nucleotides. The 3'-end terminates with a string of 18 adenine residues located 12 nucleotides downstream from an AATAAA polyadenylation signal consensus sequence. The 3'untranslated region contains 3 copies of the sequence ATTTA which is characteristic of transiently expressed genes such as GM-CSF, G-CSF, interferons, several interleukins, tumor necrosis factor, and oncogenes c-fos and c-myc (Shaw et al., Cell 46: 659, 1986); two of these repeats at nucleotide positions 461-468 and 470-477 are part of an 8 nucleotide motif TATTTATT, which is also present in many of these molecules (Caput et al., Proc. Natl. Acad. Sci. USA 83: 1670, 1986).

The predicted polypeptide encoded by the cDNA insert of clone P40.2B4 consists of 144 residues. This size estimation is based on the presumption that the first ATG in the sequence (nucleotide position 16-18) is the initiator codon, a view supported by the efficient expression of the cDNA in fibroblasts and by the presence of an adenine at nucleotide position 13, in concordance with the consensus sequence for an initiator ATG codon; an in-frame TGA translation termination codon occurs as nucleotides 448-450. The deducted P40 sequence is characterized by a hydrophobic N-terminal seuqence typical of a signal peptide. Because of the presence of a blocked N-terminus in the native protein, there is some uncertainty concerning the N-terminal residue. Based on the probability weight-matrix described, (Von Heijne, Nucleic Acid Res. 14: 4683, 1986), the most likely N-terminal sequence of the mature protein would be Gln-Arg-Cys . . . . This is consistent with evidence obtained by biochemical analysis of P40 peptides. Mature P40 would then consist of 126 amino acids with a predicted relative molecular mass of 14,150. The difference with the Mr measured for native P40 appears to be due to glycosylation as suggested by the presence of 4 potential N-linked glycosylation sites and confirmed by the about 15 kDa Mr of the native protein after N-glycanase-treatment. The sequence of P40 is further characterized by the presence of 40 cysteines and a strong predominance by cationic residues, which explains the elevated pI(10) of the native protein.

EXAMPLE 10 Isolation of the Human Genomic P40 Gene

The human genomic P40 gene was cloned using the murine P40 cDNA clone as a probe. Briefly, a human genomic library was constructed in phage λGEM11 (Promega, Madison, Wis.) with Sau3A-cut DNA isolated from an EBV-immortalized human lymphoblastoid cell line (CESS). The library was screened with a ³² P-labeled mouse P40 cDNA under low stringency hybridization conditions (two washes at 55° C. in 2x SSC and 0.1% SDS) and yielded a positive clone (λH40.3a1). Analysis of this clone identified a 900 bp HindIII fragment which encoded a region of high homology with the 3' region of the murine cDNA.

Overlapping restriction fragments from λH40.3a1 were subcloned into M13 vectors and sequenced by the dideoxynucleotide method. A 2 kb SmaI/BamHI fragment was sequenced using deletion mutants generated by digestion with exonuclease III as described by Henikoff, S. (1984) Gene 28:351. FIG. 13 depicts a restriction map of the human gene; its nucleotide and amino acid sequence are shown in FIG. 14.

EXAMPLE 11 Isolation of a Human P40 cDNA

A human cDNA library constructed in λgt10 using poly(A)⁺ RNA prepared from peripheral blood mononuclear cells (PBMC) stimulated for 24 h with phytohemagglutinin (PHA), 30 ug/ml, and phorbol myristate acetate (PMA), 100 ug/ml. The library was screened with a 0.9-kb HindIII restriction fragment of the human genomic clone described in Example 10. Filters were washed at 65° C. with 30 mM NaCl, 3 mM sodium citrate and 0.1% SDS. Screening yielded two positive clones, λcH40.2 and λcH40.4. The DNA sequence of the human P40 cDNA was deduced by dideoxynucleotide sequencing of these two clones. The nucleotide and amino acid sequences are shown under "Detailed Description of the Invention".

The human P40 cDNA has an open reading frame of 432 nucleotides specifying a polypeptide of 144 amino acids, which includes, by homology with the mouse protein, a presumptive signal peptide of 18 residues. The predicted molecular mass of the unglycosylated mature protein is 14,110 Daltons. As for mouse P40, the presence of four potential N-linked glycosylation sites makes it likely that the molecular mass of the native protein is much more elevated. The homology with mouse P40 is 69% at the nucleotide level and 55% at the protein level. Noteworthy, the 10 cysteines in the mature protein are perfectly conserved but human P40 has an additional cysteine in the presumptive signal peptide. No other homologies were detected between human P40 and previously sequenced proteins.

The size of the RNA for human P40 was determined in Northern blots of poly(A)⁺ RNA isolated from PBMC stimulated with PHA (0.5%) and PMA (100 ng/ml) for 24 hours. P40 cDNA hybridized with a band of ≈700 bp, a size comparable to that of the mouse P40 message. No message was observed in freshly isolated unstimulated PBMC.

EXAMPLE 12 Isolation of the Murine Genomic P40 Gene

The murine genomic P40 gene was cloned using the murine P40 cDNA clone as a probe. A subgenomic library was constructed in phage λGEM11 with sized fragments isolated by agarose gel electrophoresis from BamHI-digested high molecular weight DNA of murine L1210 leukemic cells. Screening with a ³² P-labeled mouse P40 cDNA yielded a positive clone (λS40.1a) which was sequenced by the dideoxynucleotide method using overlapping restriction fragments cloned in M13 vectors. FIG. 13 depicts a restriction map of the murine P40 genomic gene; its nucleotide and amino acid sequence are shown in FIG. 15.

EXAMPLE 13 Comparison of Human and Murine Genomic Genes

As indicated in FIG. 13 the murine and human genomic genes share an identical organization: they both are approximately 4 kb in length and consist of 4 introns and 5 exons flanked by consensus donor and acceptor splice sites. The complete sequence of the two genes is shown in FIGS. 14 and 15.

Although the size of each exon is identical in the two genes, their homology is somewhat variable with a minimum of 60% in the first and a maximum of 76% in the last exon. This results in a 55% homology at the amino acid level and in a perfect conservation of the 10 cysteine residues present in the two mature proteins. The introns are also very similar in size, except for intron 4, which is about 0.5 kb longer in the human gene. However, the introns show no significant homology except for intron 2, which is 69% identical in the two species. A stretch of alternating purines and pyrimidines is found in the third mouse intron (poly dA-dC) and in the fourth human intron (poly dG-dT). These sequences have a strong potential to adopt a left-handed conformation (Z-DNA), and reportedly display an enhancer-like activity [Hamada, H. (1984) Mol. Cell. Biol. 4:2622]. In the fourth intron of the human gene (nucleotides 2200-2500), an Alu sequence was identified.

The 5' flanking regions of mouse and human P40 genes contain long stretches of highly conserved sequences, indicating that the homology between the two genes is not restricted to the coding regions (FIG. 16). Both genes have a TATA-like sequence, located 57 and 56 bp upstream the ATG start codon, respectively. Several consensus motifs conceivably involved in the transcriptional control are well conserved in the two genes. Upstream of the TATA box, is one copy of the consensus binding site for AP-1, a factor involved in the regulation of genes by phorbol esters [Lee, W. et al. (1987) Cell 49:741]. This sequence (5'-TGACTCA-3') is likely to be functional in the P40 gene inasmuch as phorbol esters strongly enhance P40 expression. In both the human and the mouse genes, the AP-1 binding consensus sequence partly overlaps with a copy of the interferon regulatory factor-1 binding element (5'-AAGTGA-3') [Miyamoto, M. et al. (1988) Cell 54:903]. Farther upstream, is noted a C-rich motif, that is present in the AP-2 binding site of the SV40-enhancer [Mitchell, P. J. (1987) Cell 50:847]. Functional studies of the promoter can determine what role the latter sequences play in the regulation of P40 expression.

The 3' untranslated regions of human and mouse P40 also show significant (63%) homology (FIG. 16). The human gene contains four copies of the ATTTA sequence, which is frequently found in other transiently expressed cytokines and apparently reduces mRNA stability [Shaw, G. et al. (1986) Cell 46:659]. Three copies of this motif are conserved in the mouse gene. By contrast, the polyadenylation signal consensus sequences are not conserved.

S1 nuclease mapping of the mouse gene identified a major start of transcription centered 33 bp upstream of the ATG start codon and 24 bp downstream of the TATA-like sequence. In the human P40 gene, the main start of transcription was localized approximately 30 bp upstream of the ATG start codon and 26 bp downstream of the TATA-like sequence.

Southern blots of mouse DNA isolated from two distinct cell lines and probed with homologous P40 cDNA under high stringency showed the hybridization pattern expected from the restriction cleavage map of the P40 gene, indicating that P40 is a single copy gene in the haploid genome. Similar results were obtained for the human gene. Moreover, extensive comparisons carried out for each P40 exon and intron failed to identify significant homologies with recorded genes.

EXAMPLE 14 Expression of the P40 gene in human PBMC

No message for P40 could be detected in unstimulated PBMC but stimulation of the cells with PMA and a calcium ionophore induced strong expression of a 0.7 kb P40 mRNA that became detectable after 8 hours and reached a maximum level after ≈24 hours (FIG. 17). P40 thus appears to belong to the growing family of cytokines that are not constitutively expressed in normal PBMC but are rapidly induced after activation of the cells.

In order to examine whether P40 expression could be induced with other stimuli, we exposed PBMC to LPS or Staphylococcus aureus strain Cowan 1. No message was detected under these conditions (FIG. 18), suggesting that the P40 gene is not readily induced in monocytes and in B cells. By contrast, exposure to T cell mitogens such as PHA or anti-CD3 antibodies induced a significant P40 response. Since anti-CD3 antibodies are considered to mimick antigenic stimulation, it is likely that P40 is secreted by normal T cells in the course of their physiological response to antigen. Addition of PMA to these T cell mitogens further increased the levels of P40 mRNA although PMA by itself had no detectable effect on P40 expression. It is unlikely that this synergistic effect of PMA is due to induction of P40 in non-T cells because of the absence of P40 message in non-rosetting PBMC (FIG. 19). Therefore, these observations seem to imply that optimal P40 expression by T cells requires both protein kinase C activation and increased intracellular calcium levels.

To investigate whether P40 is elaborated by a particular subset of T lymphocytes, T cells were purified by nylon wool filtration and CD4⁺ cells separated from CD8⁺ by fluorescence-activated cell sorting. As shown in FIG. 19, P40 was preferentially expressed in the CD4⁺ subset. These results together with observations made in the mouse (Example 8) indicate that, in the immune system, P40 is essentially produced by helper T cells.

EXAMPLE 15 Expression and Biological Activity of Recombinant P40

A. Baculovirus expression system and semi-purification of recombinant P40

Recombinant human P40 was expressed in Spodoptera frugiperda S19 cells using a recombinant baculovirus. A similar expression and biological activity system was used for recombinant murine P40,

In the case of human P40, a 489 bp EcoRI-HindIII fragment of λcH40.4 was subcloned into the BamHI site located in the 5' end of the polyhedrin gene in plasmid pVL941 [Luchow, V. A. et al. (1989) Virology 170:31]. This construct was transfected along with DNA of Autographa californica nuclear polyhedrosis virus into Spodoptera frugiperda S19 cells and recombinant baculovirus clones were isolated by limiting dilution and dot hybridization as described [Summers, M. D. (1988) A Manual of Methods for Baculovirus Vectors and Insect Cell Culture Procedure. Texas Agricultural Experiment Station Bulletin No. 1555]. Expression of the recombinant protein was verified in infected cells incubated with ³⁵ S-labeled methionine. A P40-enriched fraction was obtained by adsorption of cationic proteins on sulfopropyl-Sepharose after dilution with 5 volumes of 33 mM sodium acetate, pH 5. Adsorbed proteins were eluted with 0.9M NaCl, 0.1M Tris-HCl, pH 8 and Tween-20 (10⁻⁴ vol/vol), precipitated with 10% trichloroacetic acid, and analyzed by SDS-PAGE. The recombinant protein used in the T-cell survival assay was semi-purified by adsorption to and elution from sulfopropyl-Sepharose under similar conditions and dialyzed against phosphate-buffered saline before use. The recombinant protein had an M_(r) of ≈23 kDa (FIG. 4) similar to that of mouse P40 and probably reflecting N-linked glycosylation. In the case of murine P40, N-glycanase treatment reduces this M_(r) to the predicted 14 kDa.

B: Biological Activity of Recombinant Human P40

Mouse P40 was originally identified by its capacity to induce long-term proliferation of certain murine helper T cell lines. Subsequent experiments have shown that a more frequent effect of P40 is to increase cell survival without inducing cell proliferation. Therefore the biological activity of recombinant human P40 was examined for a capacity to enhance the survival of a number of human T cell lines that had been maintained in culture in the presence of PHA, irradiated PBMC as feeders, and IL-4.

Stimulations were performed for 24 hours in RPMI 1640 medium supplemented with 10% fetal calf serum. Long-term T cell lines were derived from PBMC of hemochromatosic patients by repeated weekly stimulation with irradiated (3000 rads) allogeneic PBMC, PHA-P (30 μg/ml) and recombinant human IL4 (25 U/ml). Prolonged survival was observed with two out of 10 lines tested, demonstrating the functional integrity of recombinant human P40 expressed in insect cells (FIG. 20). It is of interest that mouse P40 also enhanced the survival of the human T cell lines, whereas human P40 was apparently not active on mouse P40-dependent cell lines.

EXAMPLE 16 Synergistic Effect of P40 and IL4 or IL3

The proliferative effects of co-culturing helper T cells in the presence of P40 and IL4 or IL3 was investigated. TUC2.15N and TUC7.41 cells (5×10⁴ /well) were cultured with suboptimal amounts of P40 in the presence or absence of a suboptimal dose of IL4 or close to optimal dose of IL3. After 3 days in culture, the cells were pulsed with tritiated thymidine. The results in Table 4 indicate that the helper T cells treated with P40 and IL4 or P40 and IL3 incorporated from about 4-40 times more thymidine than those cells treated with any one of these proteins. Thus, a strong synergy between P40 and IL4 or IL3 exists with respect to stimulating proliferation of helper T cell lines that respond to these proteins.

                  TABLE 4                                                          ______________________________________                                         Synergism between P40 and IL4 or IL3                                                   P40     IL4      IL3    Thymidine Incorpora-                           Cells   (U/ml)  (U/ml)   (ng/ml)                                                                               tion (cpm)                                     ______________________________________                                         TUC2.15N                                                                               0       0        0      122                                                    80      0        0      1296                                                   0       20       0      4446                                                   80      20       0      19248                                                  0       0        3      4781                                                   80      0        3      54366                                          TUC7.51N                                                                               0       0        0      120                                                    80      0        0      4958                                                   0       20       0      4459                                                   80      20       0      31050                                                  0       0        3      4354                                                   80      0        3      72157                                          ______________________________________                                          TUC2.15N and TUC7.51 helper T cells (5 × 10.sup.4 /well) were            cultured with suboptimal amounts of P40 in the presence or absence of a        suboptimal dose of IL4 or of an optimal dose of IL3. The cultures were         pulsed with tritiated thymidine after 3 days.                             

What is claimed is:
 1. An isolated nucleic acid molecule which encodes murine T cell growth factor P40 which supports interleukin-2 and interleukin-4 independent growth of T cells.
 2. The isolated nucleic acid molecule of claim 1, wherein said isolated nucleic acid molecule is cDNA.
 3. The isolated nucleic acid molecule of claim 1, wherein said isolated nucleic acid molecule is genomic DNA.
 4. The isolated nucleic acid molecule of claim 1, wherein said molecule is cDNA, codes for murine P40 and has nucleotide sequence: ##STR4##
 5. The nucleic acid molecule of claim 1, wherein said molecule codes for murine P40 having amino acid sequence ##STR5##
 6. The nucleic acid molecule of claim 1, wherein said molecule codes for murine P40 having amino acid sequence: ##STR6##
 7. The isolated nucleic acid molecule of claim 3, comprising the nucleotide sequence of FIG.
 15. 8. The nucleic acid molecule of claim 1, wherein said molecule is RNA.
 9. Isolated nucleic acid molecule consisting of genomic DNA which encodes human T cell growth factor P40 which supports interleukin-2 and interleukin-4 independent growth of T cells.
 10. The isolated nucleic acid molecule of claim 9, consisting of the nucleotide sequence of FIG.
 14. 11. Replicable expression vector comprising the isolated nucleic acid molecule of claim 1 operably linked to a nucleotide sequence which controls expression thereof.
 12. The replicable expression vector of claim 11, comprising a replicable prokaryotic expression vector.
 13. The replicable expression vector of claim 11, comprising a replicable eukaryotic expression vector.
 14. Microorganism transformed by the isolated nucleic acid molecule of claim
 1. 15. Microorganism transformed by the replicable expression vector of claim
 11. 16. Cell line transformed by the replicable expression vector of claim
 11. 17. Replicable expression vector comprising the isolated nucleic acid molecule of claim 9 operably linked to a nucleotide sequence which controls expression thereof.
 18. The replicable expression vector of claim 17, comprising a replicable eukaryotic expression vector.
 19. Microorganism transformed by the isolated nucleic acid molecule of claim
 9. 20. Microorganism transformed by the replicable expression vector of claim
 17. 